Systems and methods for digital photography

ABSTRACT

A system, method, and computer program product are provided for rendering a combined image. In use, two or more source images including at least one strobe image and at least one ambient image are loaded. A pixel-level correction is estimated for at least one of the two or more source images based on a pixel level correction function. At least one pixel of the two or more source images is color-corrected based on the pixel-level correction. A first blend weight associated with the two or more source images is initialized, and a first combined image from the two or more source images is rendered based on the color-correction and the first blend weight. Additional systems, methods, and computer program products are also presented.

CROSS-REFERENCES TO RELATED APPLICATIONS

The present application is a continuation of, and claims priority to,U.S. patent application Ser. No. 16/518,811, filed Jul. 22, 2019,entitled “SYSTEMS AND METHODS FOR DIGITAL PHOTOGRAPHY,” which in turn isa continuation of, and claims priority to, U.S. patent application Ser.No. 16/296,038, filed Mar. 7, 2019, entitled “SYSTEMS AND METHODS FORDIGITAL PHOTOGRAPHY,” now U.S. Pat. No. 10,375,367, which in turn is acontinuation of, and claims priority to, U.S. patent application Ser.No. 16/147,149, filed Sep. 28, 2018, entitled “SYSTEMS AND METHODS FORDIGITAL PHOTOGRAPHY”, now U.S. Pat. No. 10,284,834, which in turn is acontinuation of, and claims priority to, U.S. patent application Ser.No. 15/808,753, filed Nov. 9, 2017, entitled “SYSTEMS AND METHODS FORDIGITAL PHOTOGRAPHY”, now U.S. Pat. No. 10,110,867; which in turn is acontinuation of, and claims priority to, U.S. patent application Ser.No. 14/887,211, filed Oct. 19, 2015, entitled “SYSTEMS AND METHODS FORDIGITAL PHOTOGRAPHY”, now U.S. Pat. No. 9,924,147; which in turn is acontinuation of, and claims priority to, U.S. patent application Ser.No. 13/999,343, filed Feb. 11, 2014, entitled “Systems and Methods forDigital Photography”, now U.S. Pat. No. 9,215,433; which, in turn,claims priority to U.S. Provisional Application No. 61/850,246, titled“Systems and Methods for Digital Photography,” filed Feb. 12, 2013, theentire contents of all of which are hereby incorporated by reference forall purposes.

BACKGROUND OF THE INVENTION Field of the Invention

Embodiments of the present invention relate generally to photographicsystems, and more specifically to systems and methods for digitalphotography.

Description of the Related Art

A typical digital camera generates a digital photograph by focusing anoptical image of a scene onto an image sensor, which samples the opticalimage to generate an electronic representation of the scene. Theelectronic representation is then processed and stored as the digitalphotograph. The image sensor is configured to generate a two-dimensionalarray of color pixel values from the optical image, typically includingan independent intensity value for standard red, green, and bluewavelengths. The digital photograph is commonly viewed by a human, whoreasonably expects the digital photograph to represent the scene as ifobserved directly. To generate digital photographs having a naturalappearance, digital cameras attempt to mimic certain aspects of humanvisual perception.

One aspect of human visual perception that digital cameras mimic isdynamic adjustment to scene intensity. An iris within the human eyecloses to admit less light and opens to admit more light, allowing thehuman eye to adjust to different levels of light intensity in a scene.Digital cameras dynamically adjust to scene intensity by selecting ashutter speed, sampling sensitivity (“ISO” index of sensitivity), andlens aperture to yield a good exposure level when generating a digitalphotograph. A good exposure level generally preserves subject detailwithin the digital photograph. Modern digital cameras are typically ableto achieve good exposure level for scenes with sufficient ambientlighting.

Another aspect of human visual perception that digital cameras mimic iscolor normalization, which causes a white object to be perceived asbeing white, even under arbitrarily colored ambient illumination. Colornormalization allows a given object to be perceived as having the samecolor over a wide range of scene illumination color and thereforeaverage scene color, also referred to as white balance. For example, awhite object will be perceived as being white whether illuminated byred-dominant incandescent lamps or blue-dominant afternoon shade light.A digital camera needs to compensate for scene white balance to properlydepict the true color of an object, independent of illumination color.For example, a white object illuminated by incandescent lamps, whichinherently produce orange-tinted light, will be directly observed asbeing white. However, a digital photograph of the same white object willappear to have an orange color cast imparted by the incandescent lamps.To achieve proper white balance for a given scene, a digital cameraconventionally calculates gain values for red, green, and blue channelsand multiplies each component of each pixel within a resulting digitalphotograph by an appropriate channel gain value. By compensating forscene white balance in this way, an object will be recorded within acorresponding digital photograph as having color that is consistent witha white illumination source, regardless of the actual white balance ofthe scene. In a candle-lit scene, which is substantially red in color,the digital camera may reduce red gain, while increasing blue gain. Inthe case of afternoon shade illumination, which is substantially blue incolor, the digital camera may reduce blue gain and increase red gain.

In scenarios where a scene has sufficient ambient lighting, a typicaldigital camera is able to generate a digital photograph with goodexposure and proper white balance. One technique for implementing whitebalance compensation makes a “gray world” assumption, which states thatan average image color should naturally be gray (attenuated white). Thisassumption is generally consistent with how humans dynamically adapt toperceive color.

In certain common scenarios, ambient lighting within a scene is notsufficient to produce a properly-exposed digital photograph of the sceneor certain subject matter within the scene. In one example scenario, aphotographer may wish to photograph a subject at night in a setting thatis inadequately illuminated by incandescent or fluorescent lamps. Aphotographic strobe, such as a light-emitting diode (LED) or Xenonstrobe, is conventionally used to beneficially illuminate the subjectand achieve a desired exposure. However, the color of the strobefrequently does not match that of ambient illumination, creating adiscordant appearance between objects illuminated primarily by thestrobe and other objects illuminated primarily by ambient lighting.

For example, if ambient illumination is provided by incandescent lampshaving a substantially orange color and strobe illumination is providedby an LED having a substantially white color, then a set of gain valuesfor red, green, and blue that provides proper white balance for ambientillumination will result in an unnatural blue tint on objects primarilyilluminated by the strobe. Alternatively, a set of gain values thatprovides proper white balance for the LED will result in an overlyorange appearance for objects primarily illuminated by ambientincandescent light. A photograph taken with the LED strobe in thisscenario will either have properly colored regions that are primarilyilluminated by the strobe and improperly orange regions that areprimarily illuminated by ambient light, or improperly blue-tintedregions that are primarily illuminated by the strobe andproperly-colored regions that are primarily illuminated by ambientlight. In sum, the photograph will include regions that are unavoidablydiscordant in color because the white balance of the strobe is differentthan that of the ambient illumination.

One approach to achieving relatively consistent white balance in strobephotography is to flood a given scene with illumination from ahigh-powered strobe or multiple high-powered strobes, therebyoverpowering ambient illumination sources and forcing illumination inthe scene to the same white balance. Flooding does not correct fordiscordantly colored ambient light sources such as incandescent lamps orcandles visible within the scene. With ambient illumination sources ofvarying color overpowered, a digital camera may generate a digitalphotograph according to the color of the high-powered strobe and producean image having very good overall white balance. However, such asolution is impractical in many settings. For example, a high-poweredstrobe is not conventionally available in small consumer digital camerasor mobile devices that include a digital camera subsystem. Conventionalconsumer digital cameras have very limited strobe capacity and areincapable of flooding most scenes. Furthermore, flooding a givenenvironment with an intense pulse of strobe illumination may be overlydisruptive and socially unacceptable in many common settings, such as apublic restaurant or indoor space. As such, even when a high-poweredstrobe unit is available, flooding an entire scene may be disallowed.More commonly, a combination of partial strobe illumination and partialambient illumination is available, leading to discordant white balancewithin a resulting digital photograph.

As the foregoing illustrates, there is a need for addressing the issueof performing color balance and/or other issues associated with theprior art of photography.

SUMMARY

A system, method, and computer program product are provided forrendering a combined image. In use, two or more source images includingat least one strobe image and at least one ambient image are loaded. Apixel-level correction is estimated for at least one of the two or moresource images based on a pixel level correction function. At least onepixel of the two or more source images is color-corrected based on thepixel-level correction. A first blend weight associated with the two ormore source images is initialized, and a first combined image from thetwo or more source images is rendered based on the color-correction andthe first blend weight. Additional systems, methods, and computerprogram products are also presented.

BRIEF DESCRIPTION OF THE DRAWINGS

So that the manner in which the above recited features of the presentinvention can be understood in detail, a more particular description ofthe invention, briefly summarized above, may be had by reference toembodiments, some of which are illustrated in the appended drawings. Itis to be noted, however, that the appended drawings illustrate onlytypical embodiments of this invention and are therefore not to beconsidered limiting of its scope, for the invention may admit to otherequally effective embodiments.

FIG. 1A illustrates a digital photographic system, configured toimplement one or more aspects of the present invention;

FIG. 1B illustrates a processor complex within the digital photographicsystem, according to one embodiment of the present invention;

FIG. 1C illustrates a digital camera, according to one embodiment of thepresent invention;

FIG. 1D illustrates a mobile device, according to one embodiment of thepresent invention;

FIG. 2A illustrates a first data flow process for generating a blendedimage based on at least an ambient image and a strobe image, accordingto one embodiment of the present invention;

FIG. 2B illustrates a second data flow process for generating a blendedimage based on at least an ambient image and a strobe image, accordingto one embodiment of the present invention;

FIG. 2C illustrates a third data flow process for generating a blendedimage based on at least an ambient image and a strobe image, accordingto one embodiment of the present invention;

FIG. 2D illustrates a fourth data flow process for generating a blendedimage based on at least an ambient image and a strobe image, accordingto one embodiment of the present invention;

FIG. 3A illustrates an image blend operation for blending a strobe imagewith an ambient image to generate a blended image, according to oneembodiment of the present invention;

FIG. 3B illustrates a blend function for blending pixels associated witha strobe image and an ambient image, according to one embodiment of thepresent invention;

FIG. 3C illustrates a blend surface for blending two pixels, accordingto one embodiment of the present invention;

FIG. 3D illustrates a blend surface for blending two pixels, accordingto another embodiment of the present invention;

FIG. 3E illustrates an image blend operation for blending a strobe imagewith an ambient image to generate a blended image, according to oneembodiment of the present invention;

FIG. 4A illustrates a patch-level analysis process for generating apatch correction array, according to one embodiment of the presentinvention;

FIG. 4B illustrates a frame-level analysis process for generatingframe-level characterization data, according to one embodiment of thepresent invention;

FIG. 5A illustrates a data flow process for correcting strobe pixelcolor, according to one embodiment of the present invention;

FIG. 5B illustrates a chromatic attractor function, according to oneembodiment of the present invention;

FIG. 6 is a flow diagram of method steps for generating an adjusteddigital photograph, according to one embodiment of the presentinvention;

FIG. 7A is a flow diagram of method steps for blending a strobe imagewith an ambient image to generate a blended image, according to a firstembodiment of the present invention;

FIG. 7B is a flow diagram of method steps for blending a strobe imagewith an ambient image to generate a blended image, according to a secondembodiment of the present invention;

FIG. 8A is a flow diagram of method steps for blending a strobe imagewith an ambient image to generate a blended image, according to a thirdembodiment of the present invention;

FIG. 8B is a flow diagram of method steps for blending a strobe imagewith an ambient image to generate a blended image, according fourthembodiment of the present invention;

FIG. 9 illustrates a user interface system for generating a combinedimage, according to one embodiment of the present invention;

FIG. 10A is a flow diagram of method steps for generating a combinedimage, according to one embodiment of the present invention;

FIG. 10B is a flow diagram of a method steps for calculating arecommended UI control position for blending two different images,according to one embodiment of the present invention;

FIGS. 11A-11C illustrate a user interface configured to adapt to deviceorientation while preserving proximity of a user interface controlelement to a hand grip edge, according to embodiments of the presentinvention;

FIG. 11D illustrates a mobile device incorporating grip sensorsconfigured to detect a user grip, according to one embodiment of thepresent invention;

FIG. 11E is a flow diagram of method steps for orienting a userinterface surface with respect to a control element, according to oneembodiment of the present invention;

FIG. 12A illustrates a first user interface control selector configuredto select one active control from one or more available controls,according to embodiments of the present invention;

FIG. 12B illustrates a second user interface control selector configuredto select one active control from one or more available controls,according to embodiments of the present invention;

FIG. 12C is a flow diagram of method steps for selecting an activecontrol from one or more available control elements, according to oneembodiment of the present invention;

FIG. 13A illustrates a data flow process for selecting an ambient targetexposure coordinate, according to one embodiment of the presentinvention;

FIG. 13B is a flow diagram of method steps for selecting an ambienttarget exposure coordinate, according to one embodiment of the presentinvention;

FIG. 13C illustrates a scene having a strobe influence region, accordingto one embodiment of the present invention;

FIG. 13D illustrates a scene mask computed to preclude a strobeinfluence region, according to one embodiment of the present invention;and

FIG. 14 is a flow diagram of method steps for sampling an ambient imageand a strobe image based on computed exposure coordinates, according toone embodiment of the present invention.

DETAILED DESCRIPTION

Certain embodiments of the present invention enable digital photographicsystems having a strobe light source to beneficially preserve properwhite balance within regions of a digital photograph primarilyilluminated by the strobe light source as well as regions primarilyilluminated by an ambient light source. Proper white balance ismaintained within the digital photograph even when the strobe lightsource and an ambient light source are of discordant color. The strobelight source may comprise a light-emitting diode (LED), a Xenon tube, orany other type of technically feasible illuminator device. Certainembodiments beneficially maintain proper white balance within thedigital photograph even when the strobe light source exhibits colorshift, a typical characteristic of high-output LEDs commonly used toimplement strobe illuminators for mobile devices.

Certain other embodiments enable efficient capture of multiple relatedimages either concurrently in time, or spaced closely together in time.Each of the multiple related images may be sampled at different exposurelevels within an image sensor.

Certain other embodiments provide for a user interface configured toenable efficient management of different merge parameters associatedwith a multi-exposure image.

System Overview

FIG. 1A illustrates a digital photographic system 100, configured toimplement one or more aspects of the present invention. Digitalphotographic system 100 includes a processor complex 110 coupled to acamera unit 130. Digital photographic system 100 may also include,without limitation, a display unit 112, a set of input/output devices114, non-volatile memory 116, volatile memory 118, a wireless unit 140,and sensor devices 142, coupled to processor complex 110. In oneembodiment, a power management subsystem 120 is configured to generateappropriate power supply voltages for each electrical load elementwithin digital photographic system 100, and a battery 122 is configuredto supply electrical energy to power management subsystem 120. Battery122 may implement any technically feasible battery, including primary orrechargeable battery technologies. Alternatively, battery 122 may beimplemented as a fuel cell, or high capacity electrical capacitor.

In one embodiment, strobe unit 136 is integrated into digitalphotographic system 100 and configured to provide strobe illumination150 that is synchronized with an image capture event performed by cameraunit 130. In an alternative embodiment, strobe unit 136 is implementedas an independent device from digital photographic system 100 andconfigured to provide strobe illumination 150 that is synchronized withan image capture event performed by camera unit 130. Strobe unit 136 maycomprise one or more LED devices, one or more Xenon cavity devices, oneor more instances of another technically feasible illumination device,or any combination thereof without departing the scope and spirit of thepresent invention. In one embodiment, strobe unit 136 is directed toeither emit illumination or not emit illumination via a strobe controlsignal 138, which may implement any technically feasible signaltransmission protocol. Strobe control signal 138 may also indicate anillumination intensity level.

In one usage scenario, strobe illumination 150 comprises at least aportion of overall illumination in a scene being photographed by cameraunit 130. Optical scene information 152, which may include strobeillumination 150 reflected from objects in the scene, is focused onto animage sensor 132 as an optical image. Image sensor 132, within cameraunit 130, generates an electronic representation of the optical image.The electronic representation comprises spatial color intensityinformation, which may include different color intensity samples forred, green, and blue light. In alternative embodiments the colorintensity samples may include, without limitation, cyan, magenta, andyellow spatial color intensity information. Persons skilled in the artwill recognize that other sets of spatial color intensity informationmay be implemented without departing the scope of embodiments of thepresent invention. The electronic representation is transmitted toprocessor complex 110 via interconnect 134, which may implement anytechnically feasible signal transmission protocol.

Display unit 112 is configured to display a two-dimensional array ofpixels to form a digital image for display. Display unit 112 maycomprise a liquid-crystal display, an organic LED display, or any othertechnically feasible type of display. Input/output devices 114 mayinclude, without limitation, a capacitive touch input surface, aresistive tabled input surface, buttons, knobs, or any other technicallyfeasible device for receiving user input and converting the input toelectrical signals. In one embodiment, display unit 112 and a capacitivetouch input surface comprise a touch entry display system, andinput/output devices 114 comprise a speaker and microphone.

Non-volatile (NV) memory 116 is configured to store data when power isinterrupted. In one embodiment, NV memory 116 comprises one or moreflash memory devices. NV memory 116 may be configured to includeprogramming instructions for execution by one or more processing unitswithin processor complex 110. The programming instructions may include,without limitation, an operating system (OS), user interface (UI)modules, imaging processing and storage modules, and one or moreembodiments of techniques taught herein for generating a digitalphotograph having proper white balance in both regions illuminated byambient light and regions illuminated by the strobe unit 136. One ormore memory devices comprising NV memory 116 may be packaged as a modulethat can be installed or removed by a user. In one embodiment, volatilememory 118 comprises dynamic random access memory (DRAM) configured totemporarily store programming instructions, image data, and the likeneeded during the course of normal operation of digital photographicsystem 100. Sensor devices 142 may include, without limitation, anaccelerometer to detect motion and orientation, an electronic gyroscopeto detect motion and orientation, a magnetic flux detector to detectorientation, and a global positioning system (GPS) module to detectgeographic position.

Wireless unit 140 may include one or more digital radios configured tosend and receive digital data. In particular, wireless unit 140 mayimplement wireless standards known in the art as “WiFi” based oninstitute for electrical and electronics engineers (IEEE) standard802.11, and may implement digital cellular telephony standards for datacommunication such as the well-known “3G” and “4G” suites of standards.In one embodiment, digital photographic system 100 is configured totransmit one or more digital photographs, generated according totechniques taught herein and residing within either NV memory 116 orvolatile memory 118 to an online photographic media service via wirelessunit 140. In such a scenario, a user may possess credentials to accessthe online photographic media service and to transmit the one or moredigital photographs for storage and presentation by the onlinephotographic media service. The credentials may be stored or generatedwithin digital photographic system 100 prior to transmission of thedigital photographs. The online photographic media service may comprisea social networking service, photograph sharing service, or any otherweb-based service that provides storage and download of digitalphotographs. In certain embodiments, one or more digital photographs aregenerated by the online photographic media service according totechniques taught herein. In such embodiments, a user may upload sourceimages for processing into the one or more digital photographs.

In one embodiment, digital photographic system 100 comprises a pluralityof camera units 130 and at least one strobe unit 136 configured tosample multiple views of a scene. In one implementation, the pluralityof camera units 130 is configured to sample a wide angle to generate apanoramic photograph. In another implementation, the plurality of cameraunits 130 is configured to sample two or more narrow angles to generatea stereoscopic photograph.

FIG. 1B illustrates a processor complex 110 within digital photographicsystem 100, according to one embodiment of the present invention.Processor complex 110 includes a processor subsystem 160 and may includea memory subsystem 162. In one embodiment processor subsystem 160comprises a system on a chip (SoC) die, memory subsystem 162 comprisesone or more DRAM dies bonded to the SoC die, and processor complex 110comprises a multi-chip module (MCM) encapsulating the SoC die and theone or more DRAM dies.

Processor subsystem 160 includes at least one central processing unit(CPU) core 170, a memory interface 180, input/output interfaces unit184, and a display interface 182 coupled to an interconnect 174. The atleast one CPU core 170 is configured to execute instructions residingwithin memory subsystem 162, volatile memory 118 of FIG. 1A, NV memory116, or any combination thereof. Each of the at least one CPU core 170is configured to retrieve and store data via interconnect 174 and memoryinterface 180. Each CPU core 170 may include a data cache, and aninstruction cache. Two or more CPU cores 170 may share a data cache, aninstruction cache, or any combination thereof. In one embodiment, acache hierarchy is implemented to provide each CPU core 170 with aprivate layer one cache, and a shared layer two cache.

Graphic processing unit (GPU) cores 172 implement graphics accelerationfunctions. In one embodiment, at least one GPU core 172 comprises ahighly-parallel thread processor configured to execute multipleinstances of one or more thread programs. GPU cores 172 may beconfigured to execute multiple thread programs according to well-knownstandards such as OpenGL™, OpenCL™, CUDA™, and the like. In certainembodiments, at least one GPU core 172 implements at least a portion ofa motion estimation function, such as a well-known Harris detector or awell-known Hessian-Laplace detector. Persons skilled in the art willrecognize that such detectors may be used to provide point pairs forestimating motion between two images and a corresponding affinetransform to account for the motion. As discussed in greater detailbelow, such an affine transform may be useful in performing certainsteps related to embodiments of the present invention.

Interconnect 174 is configured to transmit data between and among memoryinterface 180, display interface 182, input/output interfaces unit 184,CPU cores 170, and GPU cores 172. Interconnect 174 may implement one ormore buses, one or more rings, a mesh, or any other technically feasibledata transmission structure or technique. Memory interface 180 isconfigured to couple memory subsystem 162 to interconnect 174. Memoryinterface 180 may also couple NV memory 116 and volatile memory 118 tointerconnect 174. Display interface 182 is configured to couple displayunit 112 to interconnect 174. Display interface 182 may implementcertain frame buffer functions such as frame refresh. Alternatively,display unit 112 may implement frame refresh. Input/output interfacesunit 184 is configured to couple various input/output devices tointerconnect 174.

FIG. 1C illustrates a digital camera 102, according to one embodiment ofthe present invention. Digital camera 102 comprises digital photographicsystem 100 packaged as a stand-alone system. As shown, a front lens forcamera unit 130 and strobe unit 136 are configured to face in the samedirection, allowing strobe unit 136 to illuminate a photographicsubject, which camera unit 130 is then able to photograph. Digitalcamera 102 includes a shutter release button 115 for triggering acapture event to be executed by the camera unit 130. Shutter releasebutton 115 represents an input device comprising input/output devices114. Other mechanisms may trigger a capture event, such as a timer. Incertain embodiments, digital camera 102 may be configured to triggerstrobe unit 136 when photographing a subject regardless of availableillumination, or to not trigger strobe unit 136 regardless of availableillumination, or to automatically trigger strobe unit 136 based onavailable illumination or other scene parameters.

FIG. 1D illustrates a mobile device 104, according to one embodiment ofthe present invention. Mobile device 104 comprises digital photographicsystem 100 and integrates additional functionality, such as cellularmobile telephony. Shutter release functions may be implemented via amechanical button or via a virtual button, which may be activated by atouch gesture on a touch entry display system within mobile device 104.Other mechanisms may trigger a capture event, such as a remote controlconfigured to transmit a shutter release command, completion of a timercount down, an audio indication, or any other technically feasible userinput event.

In alternative embodiments, digital photographic system 100 may comprisea tablet computing device, a reality augmentation device, or any othercomputing system configured to accommodate at least one instance ofcamera unit 130 and at least one instance of strobe unit 136.

Image Synthesis

FIG. 2A illustrates a first data flow process 200 for generating ablended image 280 based on at least an ambient image 220 and a strobeimage 210, according to one embodiment of the present invention. Astrobe image 210 comprises a digital photograph sampled by camera unit130 while strobe unit 136 is actively emitting strobe illumination 150.Ambient image 220 comprises a digital photograph sampled by camera unit130 while strobe unit 136 is inactive and substantially not emittingstrobe illumination 150. In other words, the ambient image 220corresponds to a first lighting condition and the strobe image 210corresponds to a second lighting condition.

In one embodiment, ambient image 220 is generated according to aprevailing ambient white balance for a scene being photographed. Theprevailing ambient white balance may be computed using the well-knowngray world model, an illuminator matching model, or any othertechnically feasible technique. Strobe image 210 should be generatedaccording to an expected white balance for strobe illumination 150,emitted by strobe unit 136. Blend operation 270, discussed in greaterdetail below, blends strobe image 210 and ambient image 220 to generatea blended image 280 via preferential selection of image data from strobeimage 210 in regions of greater intensity compared to correspondingregions of ambient image 220.

In one embodiment, data flow process 200 is performed by processorcomplex 110 within digital photographic system 100, and blend operation270 is performed by at least one GPU core 172, one CPU core 170, or anycombination thereof.

FIG. 2B illustrates a second data flow process 202 for generating ablended image 280 based on at least an ambient image 220 and a strobeimage 210, according to one embodiment of the present invention. Strobeimage 210 comprises a digital photograph sampled by camera unit 130while strobe unit 136 is actively emitting strobe illumination 150.Ambient image 220 comprises a digital photograph sampled by camera unit130 while strobe unit 136 is inactive and substantially not emittingstrobe illumination 150.

In one embodiment, ambient image 220 is generated according to aprevailing ambient white balance for a scene being photographed. Theprevailing ambient white balance may be computed using the well-knowngray world model, an illuminator matching model, or any othertechnically feasible technique. In certain embodiments, strobe image 210is generated according to the prevailing ambient white balance. In analternative embodiment ambient image 220 is generated according to aprevailing ambient white balance, and strobe image 210 is generatedaccording to an expected white balance for strobe illumination 150,emitted by strobe unit 136. In other embodiments, ambient image 210 andstrobe image 220 comprise raw image data, having no white balanceoperation applied to either. Blended image 280 may be subjected toarbitrary white balance operations, as is common practice with raw imagedata, while advantageously retaining color consistency between regionsdominated by ambient illumination and regions dominated by strobeillumination.

As a consequence of color balance differences between ambientillumination, which may dominate certain portions of strobe image 210and strobe illumination 150, which may dominate other portions of strobeimage 210, strobe image 210 may include color information in certainregions that is discordant with color information for the same regionsin ambient image 220. Frame analysis operation 240 and color correctionoperation 250 together serve to reconcile discordant color informationwithin strobe image 210. Frame analysis operation 240 generates colorcorrection data 242, described in greater detail below, for adjustingcolor within strobe image 210 to converge spatial color characteristicsof strobe image 210 to corresponding spatial color characteristics ofambient image 220. Color correction operation 250 receives colorcorrection data 242 and performs spatial color adjustments to generatecorrected strobe image data 252 from strobe image 210. Blend operation270, discussed in greater detail below, blends corrected strobe imagedata 252 with ambient image 220 to generate blended image 280. Colorcorrection data 242 may be generated to completion prior to colorcorrection operation 250 being performed. Alternatively, certainportions of color correction data 242, such as spatial correctionfactors, may be generated as needed.

In one embodiment, data flow process 202 is performed by processorcomplex 110 within digital photographic system 100. In certainimplementations, blend operation 270 and color correction operation 250are performed by at least one GPU core 172, at least one CPU core 170,or a combination thereof. Portions of frame analysis operation 240 maybe performed by at least one GPU core 172, one CPU core 170, or anycombination thereof. Frame analysis operation 240 and color correctionoperation 250 are discussed in greater detail below.

FIG. 2C illustrates a third data flow process 204 for generating ablended image 280 based on at least an ambient image 220 and a strobeimage 210, according to one embodiment of the present invention. Strobeimage 210 comprises a digital photograph sampled by camera unit 130while strobe unit 136 is actively emitting strobe illumination 150.Ambient image 220 comprises a digital photograph sampled by camera unit130 while strobe unit 136 is inactive and substantially not emittingstrobe illumination 150.

In one embodiment, ambient image 220 is generated according to aprevailing ambient white balance for a scene being photographed. Theprevailing ambient white balance may be computed using the well-knowngray world model, an illuminator matching model, or any othertechnically feasible technique. Strobe image 210 should be generatedaccording to an expected white balance for strobe illumination 150,emitted by strobe unit 136.

In certain common settings, camera unit 130 resides within a hand-helddevice, which may be subject to a degree of involuntary random movementor “shake” while being held in a user's hand. In these settings, whenthe hand-held device sequentially samples two images, such as strobeimage 210 and ambient image 220, the effect of shake may causemisalignment between the two images. The two images should be alignedprior to blend operation 270, discussed in greater detail below.Alignment operation 230 generates an aligned strobe image 232 fromstrobe image 210 and an aligned ambient image 234 from ambient image220. Alignment operation 230 may implement any technically feasibletechnique for aligning images or sub-regions.

In one embodiment, alignment operation 230 comprises an operation todetect point pairs between strobe image 210 and ambient image 220, anoperation to estimate an affine or related transform needed tosubstantially align the point pairs. Alignment may then be achieved byexecuting an operation to resample strobe image 210 according to theaffine transform thereby aligning strobe image 210 to ambient image 220,or by executing an operation to resample ambient image 220 according tothe affine transform thereby aligning ambient image 220 to strobe image210. Aligned images typically overlap substantially with each other, butmay also have non-overlapping regions. Image information may bediscarded from non-overlapping regions during an alignment operation.Such discarded image information should be limited to relatively narrowboundary regions. In certain embodiments, resampled images arenormalized to their original size via a scaling operation performed byone or more GPU cores 172.

In one embodiment, the point pairs are detected using a technique knownin the art as a Harris affine detector. The operation to estimate anaffine transform may compute a substantially optimal affine transformbetween the detected point pairs, comprising pairs of reference pointsand offset points. In one implementation, estimating the affinetransform comprises computing a transform solution that minimizes a sumof distances between each reference point and each offset pointsubjected to the transform. Persons skilled in the art will recognizethat these and other techniques may be implemented for performing thealignment operation 230 without departing the scope and spirit of thepresent invention.

In one embodiment, data flow process 204 is performed by processorcomplex 110 within digital photographic system 100. In certainimplementations, blend operation 270 and resampling operations areperformed by at least one GPU core.

FIG. 2D illustrates a fourth data flow process 206 for generating ablended image 280 based on at least an ambient image 220 and a strobeimage 210, according to one embodiment of the present invention. Strobeimage 210 comprises a digital photograph sampled by camera unit 130while strobe unit 136 is actively emitting strobe illumination 150.Ambient image 220 comprises a digital photograph sampled by camera unit130 while strobe unit 136 is inactive and substantially not emittingstrobe illumination 150.

In one embodiment, ambient image 220 is generated according to aprevailing ambient white balance for a scene being photographed. Theprevailing ambient white balance may be computed using the well-knowngray world model, an illuminator matching model, or any othertechnically feasible technique. In certain embodiments, strobe image 210is generated according to the prevailing ambient white balance. In analternative embodiment ambient image 220 is generated according to aprevailing ambient white balance, and strobe image 210 is generatedaccording to an expected white balance for strobe illumination 150,emitted by strobe unit 136. In other embodiments, ambient image 210 andstrobe image 220 comprise raw image data, having no white balanceoperation applied to either. Blended image 280 may be subjected toarbitrary white balance operations, as is common practice with raw imagedata, while advantageously retaining color consistency between regionsdominated by ambient illumination and regions dominated by strobeillumination.

Alignment operation 230, discussed previously in FIG. 2C, generates analigned strobe image 232 from strobe image 210 and an aligned ambientimage 234 from ambient image 220. Alignment operation 230 may implementany technically feasible technique for aligning images.

Frame analysis operation 240 and color correction operation 250, bothdiscussed previously in FIG. 2B, operate together to generate correctedstrobe image data 252 from aligned strobe image 232. Blend operation270, discussed in greater detail below, blends corrected strobe imagedata 252 with ambient image 220 to generate blended image 280.

Color correction data 242 may be generated to completion prior to colorcorrection operation 250 being performed. Alternatively, certainportions of color correction data 242, such as spatial correctionfactors, may be generated as needed. In one embodiment, data flowprocess 206 is performed by processor complex 110 within digitalphotographic system 100.

While frame analysis operation 240 is shown operating on aligned strobeimage 232 and aligned ambient image 234, certain global correctionfactors may be computed from strobe image 210 and ambient image 220. Forexample, in one embodiment, a frame-level color correction factor,discussed below, may be computed from strobe image 210 and ambient image220. In such an embodiment the frame-level color correction may beadvantageously computed in parallel with alignment operation 230,reducing overall time required to generate blended image 280.

In certain embodiments, strobe image 210 and ambient image 220 arepartitioned into two or more tiles and color correction operation 250,blend operation 270, and resampling operations comprising alignmentoperation 230 are performed on a per tile basis before being combinedinto blended image 280. Persons skilled in the art will recognize thattiling may advantageously enable finer grain scheduling of computationaltasks among CPU cores 170 and GPU cores 172. Furthermore, tiling enablesGPU cores 172 to advantageously operate on images having higherresolution in one or more dimensions than native two-dimensional surfacesupport may allow for the GPU cores. For example, certain generations ofGPU core are only configured to operate on 2048 by 2048 pixel images,but popular mobile devices include camera resolution of more than 2048in one dimension and less than 2048 in another dimension. In such asystem, two tiles may be used to partition strobe image 210 and ambientimage 220 into two tiles each, thereby enabling a GPU having aresolution limitation of 2048 by 2048 to operate on the images. In oneembodiment, a first of tile blended image 280 is computed to completionbefore a second tile for blended image 280 is computed, thereby reducingpeak system memory required by processor complex 110.

FIG. 3A illustrates image blend operation 270, according to oneembodiment of the present invention. A strobe image 310 and an ambientimage 320 of the same horizontal resolution (H-res) and verticalresolution (V-res) are combined via blend function 330 to generateblended image 280 having the same horizontal resolution and verticalresolution. In alternative embodiments, strobe image 310 or ambientimage 320, or both images may be scaled to an arbitrary resolutiondefined by blended image 280 for processing by blend function 330. Blendfunction 330 is described in greater detail below in FIGS. 3B-3D.

As shown, strobe pixel 312 and ambient pixel 322 are blended by blendfunction 330 to generate blended pixel 332, stored in blended image 280.Strobe pixel 312, ambient pixel 322, and blended pixel 332 are locatedin substantially identical locations in each respective image.

In one embodiment, strobe image 310 corresponds to strobe image 210 ofFIG. 2A and ambient image 320 corresponds to ambient image 220. Inanother embodiment, strobe image 310 corresponds to corrected strobeimage data 252 of FIG. 2B and ambient image 320 corresponds to ambientimage 220. In yet another embodiment, strobe image 310 corresponds toaligned strobe image 232 of FIG. 2C and ambient image 320 corresponds toaligned ambient image 234. In still yet another embodiment, strobe image310 corresponds to corrected strobe image data 252 of FIG. 2D, andambient image 320 corresponds to aligned ambient image 234.

Blend operation 270 may be performed by one or more CPU cores 170, oneor more GPU cores 172, or any combination thereof. In one embodiment,blend function 330 is associated with a fragment shader, configured toexecute within one or more GPU cores 172.

FIG. 3B illustrates blend function 330 of FIG. 3A for blending pixelsassociated with a strobe image and an ambient image, according to oneembodiment of the present invention. As shown, a strobe pixel 312 fromstrobe image 310 and an ambient pixel 322 from ambient image 320 areblended to generate a blended pixel 332 associated with blended image280.

Strobe intensity 314 is calculated for strobe pixel 312 by intensityfunction 340. Similarly, ambient intensity 324 is calculated byintensity function 340 for ambient pixel 322. In one embodiment,intensity function 340 implements Equation 1, where Cr, Cg, Cb arecontribution constants and Red, Green, and Blue represent colorintensity values for an associated pixel:

Intensity=Cr*Red+Cg*Green+Cb*Blue  (Eq. 1)

A sum of the contribution constants should be equal to a maximum rangevalue for Intensity. For example, if Intensity is defined to range from0.0 to 1.0, then Cr+Cg+Cb=1.0. In one embodiment Cr=Cg=Cb=1/3.

Blend value function 342 receives strobe intensity 314 and ambientintensity 324 and generates a blend value 344. Blend value function 342is described in greater detail in FIGS. 3B and 3C. In one embodiment,blend value 344 controls a linear mix operation 346 between strobe pixel312 and ambient pixel 322 to generate blended pixel 332. Linear mixoperation 346 receives Red, Green, and Blue values for strobe pixel 312and ambient pixel 322. Linear mix operation 346 receives blend value344, which determines how much strobe pixel 312 versus how much ambientpixel 322 will be represented in blended pixel 332. In one embodiment,linear mix operation 346 is defined by equation 2, where Out correspondsto blended pixel 332, Blend corresponds to blend value 344, “A”corresponds to a color vector comprising ambient pixel 322, and “B”corresponds to a color vector comprising strobe pixel 312.

Out=(Blend*B)+(1.0−Blend)*A  (Eq. 2)

When blend value 344 is equal to 1.0, blended pixel 332 is entirelydetermined by strobe pixel 312. When blend value 344 is equal to 0.0,blended pixel 332 is entirely determined by ambient pixel 322. Whenblend value 344 is equal to 0.5, blended pixel 332 represents a percomponent average between strobe pixel 312 and ambient pixel 322.

FIG. 3C illustrates a blend surface 302 for blending two pixels,according to one embodiment of the present invention. In one embodiment,blend surface 302 defines blend value function 342 of FIG. 3B. Blendsurface 302 comprises a strobe dominant region 352 and an ambientdominant region 350 within a coordinate system defined by an axis foreach of ambient intensity 324, strobe intensity 314, and blend value344. Blend surface 302 is defined within a volume where ambientintensity 324, strobe intensity 314, and blend value 344 may range from0.0 to 1.0. Persons skilled in the art will recognize that a range of0.0 to 1.0 is arbitrary and other numeric ranges may be implementedwithout departing the scope and spirit of the present invention.

When ambient intensity 324 is larger than strobe intensity 314, blendvalue 344 may be defined by ambient dominant region 350. Otherwise, whenstrobe intensity 314 is larger than ambient intensity 324, blend value344 may be defined by strobe dominant region 352. Diagonal 351delineates a boundary between ambient dominant region 350 and strobedominant region 352, where ambient intensity 324 is equal to strobeintensity 314. As shown, a discontinuity of blend value 344 in blendsurface 302 is implemented along diagonal 351, separating ambientdominant region 350 and strobe dominant region 352.

For simplicity, a particular blend value 344 for blend surface 302 willbe described herein as having a height above a plane that intersectsthree points including points at (1,0,0), (0,1,0), and the origin(0,0,0). In one embodiment, ambient dominant region 350 has a height 359at the origin and strobe dominant region 352 has a height 358 aboveheight 359. Similarly, ambient dominant region 350 has a height 357above the plane at location (1,1), and strobe dominant region 352 has aheight 356 above height 357 at location (1,1). Ambient dominant region350 has a height 355 at location (1,0) and strobe dominant region 352has a height of 354 at location (0,1).

In one embodiment, height 355 is greater than 0.0, and height 354 isless than 1.0. Furthermore, height 357 and height 359 are greater than0.0 and height 356 and height 358 are each greater than 0.25. In certainembodiments, height 355 is not equal to height 359 or height 357.Furthermore, height 354 is not equal to the sum of height 356 and height357, nor is height 354 equal to the sum of height 358 and height 359.

The height of a particular point within blend surface 302 defines blendvalue 344, which then determines how much strobe pixel 312 and ambientpixel 322 each contribute to blended pixel 332. For example, at location(0,1), where ambient intensity is 0.0 and strobe intensity is 1.0, theheight of blend surface 302 is given as height 354, which sets blendvalue 344 to a value for height 354. This value is used as blend value344 in mix operation 346 to mix strobe pixel 312 and ambient pixel 322.At (0,1), strobe pixel 312 dominates the value of blended pixel 332,with a remaining, small portion of blended pixel 322 contributed byambient pixel 322. Similarly, at (1,0), ambient pixel 322 dominates thevalue of blended pixel 332, with a remaining, small portion of blendedpixel 322 contributed by strobe pixel 312.

[woo] Ambient dominant region 350 and strobe dominant region 352 areillustrated herein as being planar sections for simplicity. However, asshown in FIG. 3D, certain curvature may be added, for example, toprovide smoother transitions, such as along at least portions ofdiagonal 351, where strobe pixel 312 and ambient pixel 322 have similarintensity. A gradient, such as a table top or a wall in a given scene,may include a number of pixels that cluster along diagonal 351. Thesepixels may look more natural if the height difference between ambientdominant region 350 and strobe dominant region 352 along diagonal 351 isreduced compared to a planar section. A discontinuity along diagonal 351is generally needed to distinguish pixels that should be strobe dominantversus pixels that should be ambient dominant. A given quantization ofstrobe intensity 314 and ambient intensity 324 may require a certainbias along diagonal 351, so that either ambient dominant region 350 orstrobe dominant region 352 comprises a larger area within the plane thanthe other.

FIG. 3D illustrates a blend surface 304 for blending two pixels,according to another embodiment of the present invention. Blend surface304 comprises a strobe dominant region 352 and an ambient dominantregion 350 within a coordinate system defined by an axis for each ofambient intensity 324, strobe intensity 314, and blend value 344. Blendsurface 304 is defined within a volume substantially identical to blendsurface 302 of FIG. 3E.

As shown, upward curvature at the origin (0,0) and at (1,1) is added toambient dominant region 350, and downward curvature at (0,0) and (1,1)is added to strobe dominant region 352. As a consequence, a smoothertransition may be observed within blended image 280 for very bright andvery dark regions, where color may be less stable and may divergebetween strobe image 310 and ambient image 320. Upward curvature may beadded to ambient dominant region 350 along diagonal 351 andcorresponding downward curvature may be added to strobe dominant region352 along diagonal 351.

In certain embodiments, downward curvature may be added to ambientdominant region 350 at (1,0), or along a portion of the axis for ambientintensity 324. Such downward curvature may have the effect of shiftingthe weight of mix operation 346 to favor ambient pixel 322 when acorresponding strobe pixel 312 has very low intensity.

In one embodiment, a blend surface, such as blend surface 302 or blendsurface 304, is pre-computed and stored as a texture map that isestablished as an input to a fragment shader configured to implementblend operation 270. A surface function that describes a blend surfacehaving an ambient dominant region 350 and a strobe dominant region 352is implemented to generate and store the texture map. The surfacefunction may be implemented on a CPU core 170 of FIG. 1A or a GPU core172, or a combination thereof. The fragment shader executing on a GPUcore may use the texture map as a lookup table implementation of blendvalue function 342. In alternative embodiments, the fragment shaderimplements the surface function and computes a blend value 344 as neededfor each combination of a strobe intensity 314 and an ambient intensity324. One exemplary surface function that may be used to compute a blendvalue 344 (blendValue) given an ambient intensity 324 (ambient) and astrobe intensity 314 (strobe) is illustrated below as pseudo-code inTable 1. A constant “e” is set to a value that is relatively small, suchas a fraction of a quantization step for ambient or strobe intensity, toavoid dividing by zero. Height 355 corresponds to constant 0.125 dividedby 3.0.

TABLE 1 fDivA = strobe/(ambient + e); fDivB = (1.0 − ambient) / ((1.0 −strobe) + (1.0 − ambient) + e) temp = (fDivA >= 1.0) ? 1.0 : 0.125;blendValue = (temp + 2.0 * fDivB) / 3.0;

In certain embodiments, the blend surface is dynamically configuredbased on image properties associated with a given strobe image 310 andcorresponding ambient image 320. Dynamic configuration of the blendsurface may include, without limitation, altering one or more of heights354 through 359, altering curvature associated with one or more ofheights 354 through 359, altering curvature along diagonal 351 forambient dominant region 350, altering curvature along diagonal 351 forstrobe dominant region 352, or any combination thereof.

One embodiment of dynamic configuration of a blend surface involvesadjusting heights associated with the surface discontinuity alongdiagonal 351. Certain images disproportionately include gradient regionshaving strobe pixels 312 and ambient pixels 322 of similar or identicalintensity. Regions comprising such pixels may generally appear morenatural as the surface discontinuity along diagonal 351 is reduced. Suchimages may be detected using a heat-map of ambient intensity 324 andstrobe intensity 314 pairs within a surface defined by ambient intensity324 and strobe intensity 314. Clustering along diagonal 351 within theheat-map indicates a large incidence of strobe pixels 312 and ambientpixels 322 having similar intensity within an associated scene. In oneembodiment, clustering along diagonal 351 within the heat-map indicatesthat the blend surface should be dynamically configured to reduce theheight of the discontinuity along diagonal 351. Reducing the height ofthe discontinuity along diagonal 351 may be implemented via addingdownward curvature to strobe dominant region 352 along diagonal 351,adding upward curvature to ambient dominant region 350 along diagonal351, reducing height 358, reducing height 356, or any combinationthereof. Any technically feasible technique may be implemented to adjustcurvature and height values without departing the scope and spirit ofthe present invention. Furthermore, any region of blend surface 302 maybe dynamically adjusted in response to image characteristics withoutdeparting the scope of the present invention.

In one embodiment, dynamic configuration of the blend surface comprisesmixing blend values from two or more pre-computed lookup tablesimplemented as texture maps. For example, a first blend surface mayreflect a relatively large discontinuity and relatively large values forheights 356 and 358, while a second blend surface may reflect arelatively small discontinuity and relatively small values for height356 and 358. Here, blend surface 304 may be dynamically configured as aweighted sum of blend values from the first blend surface and the secondblend surface. Weighting may be determined based on certain imagecharacteristics, such as clustering of strobe intensity 314 and ambientintensity 324 pairs in certain regions within the surface defined bystrobe intensity 314 and ambient intensity 324, or certain histogramattributes for strobe image 210 and ambient image 220. In oneembodiment, dynamic configuration of one or more aspects of the blendsurface, such as discontinuity height, may be adjusted according todirect user input, such as via a UI tool.

FIG. 3E illustrates an image blend operation 270 for blending a strobeimage with an ambient image to generate a blended image, according toone embodiment of the present invention. A strobe image 310 and anambient image 320 of the same horizontal resolution and verticalresolution are combined via mix operation 346 to generate blended image280 having the same resolution horizontal resolution and verticalresolution. In alternative embodiments, strobe image 310 or ambientimage 320, or both images may be scaled to an arbitrary resolutiondefined by blended image 280 for processing by mix operation 346.

In certain settings, strobe image 310 and ambient image 320 include aregion of pixels having similar intensity per pixel but different colorper pixel. Differences in color may be attributed to differences inwhite balance for each image and different illumination contribution foreach image. Because the intensity among adjacent pixels is similar,pixels within the region will cluster along diagonal 351 of FIGS. 3B and3C, resulting in a distinctly unnatural speckling effect as adjacentpixels are weighted according to either strobe dominant region 352 orambient dominant region 350. To soften this speckling effect and producea natural appearance within these regions, blend values may be blurred,effectively reducing the discontinuity between strobe dominant region352 and ambient dominant region 350. As is well-known in the art,blurring may be implemented by combining two or more individual samples.

In one embodiment, a blend buffer 315 comprises blend values 345, whichare computed from a set of two or more blend samples. Each blend sampleis computed according to blend function 330, described previously inconjunction with FIGS. 3B-3D. In one embodiment, blend buffer 315 isfirst populated with blend samples, computed according to blend function330. The blend samples are then blurred to compute each blend value 345,which is stored to blend buffer 315. In other embodiments, a first blendbuffer is populated with blend samples computed according to blendfunction 330, and two or more blend samples from the first blend bufferare blurred together to generate blend each value 345, which is storedin blend buffer 315. In yet other embodiments, two or more blend samplesfrom the first blend buffer are blurred together to generate each blendvalue 345 as needed. In still another embodiment, two or more pairs ofstrobe pixels 312 and ambient pixels 322 are combined to generate eachblend value 345 as needed. Therefore, in certain embodiments, blendbuffer 315 comprises an allocated buffer in memory, while in otherembodiments blend buffer 315 comprises an illustrative abstraction withno corresponding allocation in memory.

As shown, strobe pixel 312 and ambient pixel 322 are mixed based onblend value 345 to generate blended pixel 332, stored in blended image280. Strobe pixel 312, ambient pixel 322, and blended pixel 332 arelocated in substantially identical locations in each respective image.

In one embodiment, strobe image 310 corresponds to strobe image 210 andambient image 320 corresponds to ambient image 220. In otherembodiments, strobe image 310 corresponds to aligned strobe image 232and ambient image 320 corresponds to aligned ambient image 234. In oneembodiment, mix operation 346 is associated with a fragment shader,configured to execute within one or more GPU cores 172.

As discussed previously in FIGS. 2B and 2D, strobe image 210 may need tobe processed to correct color that is divergent from color incorresponding ambient image 220. Strobe image 210 may includeframe-level divergence, spatially localized divergence, or a combinationthereof. FIGS. 4A and 4B describe techniques implemented in frameanalysis operation 240 for computing color correction data 242. Incertain embodiments, color correction data 242 comprises frame-levelcharacterization data for correcting overall color divergence, andpatch-level correction data for correcting localized color divergence.FIGS. 5A and 5B discuss techniques for implementing color correctionoperation 250, based on color correction data 242.

FIG. 4A illustrates a patch-level analysis process 400 for generating apatch correction array 450, according to one embodiment of the presentinvention. Patch-level analysis provides local color correctioninformation for correcting a region of a source strobe image to beconsistent in overall color balance with an associated region of asource ambient image. A patch corresponds to a region of one or morepixels within an associated source image. A strobe patch 412 comprisesrepresentative color information for a region of one or more pixelswithin strobe patch array 410, and an associated ambient patch 422comprises representative color information for a region of one or morepixels at a corresponding location within ambient patch array 420.

In one embodiment, strobe patch array 410 and ambient patch array 420are processed on a per patch basis by patch-level correction estimator430 to generate patch correction array 450. Strobe patch array 410 andambient patch array 420 each comprise a two-dimensional array ofpatches, each having the same horizontal patch resolution and the samevertical patch resolution. In alternative embodiments, strobe patcharray 410 and ambient patch array 420 may each have an arbitraryresolution and each may be sampled according to a horizontal andvertical resolution for patch correction array 450.

In one embodiment, patch data associated with strobe patch array 410 andambient patch array 420 may be pre-computed and stored for substantiallyentire corresponding source images. Alternatively, patch data associatedwith strobe patch array 410 and ambient patch array 420 may be computedas needed, without allocating buffer space for strobe patch array 410 orambient patch array 420.

In data flow process 202 of FIG. 2B, the source strobe image comprisesstrobe image 210, while in data flow process 206 of FIG. 2D, the sourcestrobe image comprises aligned strobe image 232. Similarly, ambientpatch array 420 comprises a set of patches generated from a sourceambient image. In data flow process 202, the source ambient imagecomprises ambient image 220, while in data flow process 206, the sourceambient image comprises aligned ambient image 234.

In one embodiment, representative color information for each patchwithin strobe patch array 410 is generated by averaging color for afour-by-four region of pixels from the source strobe image at acorresponding location, and representative color information for eachpatch within ambient patch array 420 is generated by averaging color fora four-by-four region of pixels from the ambient source image at acorresponding location. An average color may comprise red, green andblue components. Each four-by-four region may be non-overlapping oroverlapping with respect to other four-by-four regions. In otherembodiments, arbitrary regions may be implemented. Patch-levelcorrection estimator 430 generates patch correction 432 from strobepatch 412 and a corresponding ambient patch 422. In certain embodiments,patch correction 432 is saved to patch correction array 450 at acorresponding location. In one embodiment, patch correction 432 includescorrection factors for red, green, and blue, computed according to thepseudo-code of Table 2, below.

TABLE 2 ratio.r = (ambient.r) / (strobe.r); ratio.g = (ambient.g) /(strobe.g); ratio.b = (ambient.b) / (strobe.b); maxRatio = max(ratio.r,max(ratio.g, ratio.b)); correct.r = (ratio.r / maxRatio); correct.g =(ratio.g / maxRatio); correct.b = (ratio.b / maxRatio);

Here, “strobe.r” refers to a red component for strobe patch 412,“strobe.g” refers to a green component for strobe patch 412, and“strobe.b” refers to a blue component for strobe patch 412. Similarly,“ambient.r,” “ambient.g,” and “ambient.b” refer respectively to red,green, and blue components of ambient patch 422. A maximum ratio ofambient to strobe components is computed as “maxRatio,” which is thenused to generate correction factors, including “correct.r” for a redchannel, “correct.g” for a green channel, and “correct.b” for a bluechannel. Correction factors correct.r, correct.g, and correct.b togethercomprise patch correction 432. These correction factors, when appliedfully in color correction operation 250, cause pixels associated withstrobe patch 412 to be corrected to reflect a color balance that isgenerally consistent with ambient patch 422.

In one alternative embodiment, each patch correction 432 comprises aslope and an offset factor for each one of at least red, green, and bluecomponents. Here, components of source ambient image pixels bounded by apatch are treated as function input values and corresponding componentsof source strobe image pixels are treated as function outputs for acurve fitting procedure that estimates slope and offset parameters forthe function. For example, red components of source ambient image pixelsassociated with a given patch may be treated as “X” values andcorresponding red pixel components of source strobe image pixels may betreated as “Y” values, to form (X,Y) points that may be processedaccording to a least-squares linear fit procedure, thereby generating aslope parameter and an offset parameter for the red component of thepatch. Slope and offset parameters for green and blue components may becomputed similarly. Slope and offset parameters for a component describea line equation for the component. Each patch correction 432 includesslope and offset parameters for at least red, green, and bluecomponents. Conceptually, pixels within an associated strobe patch maybe color corrected by evaluating line equations for red, green, and bluecomponents.

In a different alternative embodiment, each patch correction 432comprises three parameters describing a quadratic function for each oneof at least red, green, and blue components. Here, components of sourcestrobe image pixels bounded by a patch are fit against correspondingcomponents of source ambient image pixels to generate quadraticparameters for color correction. Conceptually, pixels within anassociated strobe patch may be color corrected by evaluating quadraticequations for red, green, and blue components.

FIG. 4B illustrates a frame-level analysis process 402 for generatingframe-level characterization data 492, according to one embodiment ofthe present invention. Frame-level correction estimator 490 reads strobedata 472 comprising pixels from strobe image data 470 and ambient data482 comprising pixels from ambient image data 480 to generateframe-level characterization data 492.

In certain embodiments, strobe data 472 comprises pixels from strobeimage 210 of FIG. 2A and ambient data 482 comprises pixels from ambientimage 220. In other embodiments, strobe data 472 comprises pixels fromaligned strobe image 232 of FIG. 2C, and ambient data 482 comprisespixels from aligned ambient image 234. In yet other embodiments, strobedata 472 comprises patches representing average color from strobe patcharray 410, and ambient data 482 comprises patches representing averagecolor from ambient patch array 420.

In one embodiment, frame-level characterization data 492 includes atleast frame-level color correction factors for red correction, greencorrection, and blue correction. Frame-level color correction factorsmay be computed according to the pseudo-code of Table 3.

TABLE 3 ratioSum.r = (ambientSum.r) / (strobeSum.r); ratioSum.g =(ambientSum.g) / (strobeSum.g); ratioSum.b = (ambientSum.b) /(strobeSum.b); maxSumRatio = max(ratioSum.r, max(ratioSum.g,ratioSum.b)); correctFrame.r = (ratioSum.r / maxSumRatio);correctFrame.g = (ratioSum.g / maxSumRatio); correctFrame.b =(ratioSum.b / maxSumRatio);

Here, “strobeSum.r” refers to a sum of red components taken over strobeimage data 470, “strobeSum.g” refers to a sum of green components takenover strobe image data 470, and “strobeSum.b” refers to a sum of bluecomponents taken over strobe image data 470. Similarly, “ambientSum.r,”“ambientSum.g,” and “ambientSum.b” each refer to a sum of componentstaken over ambient image data 480 for respective red, green, and bluecomponents. A maximum ratio of ambient to strobe sums is computed as“maxSumRatio,” which is then used to generate frame-level colorcorrection factors, including “correctFrame.r” for a red channel,“correctFrame.g” for a green channel, and “correctFrame.b” for a bluechannel. These frame-level color correction factors, when applied fullyand exclusively in color correction operation 250, cause overall colorbalance of strobe image 210 to be corrected to reflect a color balancethat is generally consistent with that of ambient image 220.

While overall color balance for strobe image 210 may be corrected toreflect overall color balance of ambient image 220, a resulting colorcorrected rendering of strobe image 210 based only on frame-level colorcorrection factors may not have a natural appearance and will likelyinclude local regions with divergent color with respect to ambient image220. Therefore, as described below in FIG. 5A, patch-level correctionmay be used in conjunction with frame-level correction to generate acolor corrected strobe image.

In one embodiment, frame-level characterization data 492 also includesat least a histogram characterization of strobe image data 470 and ahistogram characterization of ambient image data 480. Histogramcharacterization may include identifying a low threshold intensityassociated with a certain low percentile of pixels, a median thresholdintensity associated with a fiftieth percentile of pixels, and a highthreshold intensity associated with a high threshold percentile ofpixels. In one embodiment, the low threshold intensity is associatedwith an approximately fifteenth percentile of pixels and a highthreshold intensity is associated with an approximately eighty-fifthpercentile of pixels, so that approximately fifteen percent of pixelswithin an associated image have a lower intensity than a calculated lowthreshold intensity and approximately eighty-five percent of pixels havea lower intensity than a calculated high threshold intensity.

In certain embodiments, frame-level characterization data 492 alsoincludes at least a heat-map, described previously. The heat-map may becomputed using individual pixels or patches representing regions ofpixels. In one embodiment, the heat-map is normalized using a logarithmoperator, configured to normalize a particular heat-map location againsta logarithm of a total number of points contributing to the heat-map.Alternatively, frame-level characterization data 492 includes a factorthat summarizes at least one characteristic of the heat-map, such as adiagonal clustering factor to quantify clustering along diagonal 351 ofFIGS. 3C and 3D. This diagonal clustering factor may be used todynamically configure a given blend surface.

While frame-level and patch-level correction coefficients have beendiscussed representing two different spatial extents, persons skilled inthe art will recognize that more than two levels of spatial extent maybe implemented without departing the scope and spirit of the presentinvention.

FIG. 5A illustrates a data flow process 500 for correcting strobe pixelcolor, according to one embodiment of the present invention. A strobepixel 520 is processed to generate a color corrected strobe pixel 512.In one embodiment, strobe pixel 520 comprises a pixel associated withstrobe image 210 of FIG. 2B, ambient pixel 522 comprises a pixelassociated with ambient image 220, and color corrected strobe pixel 512comprises a pixel associated with corrected strobe image data 252. In analternative embodiment, strobe pixel 520 comprises a pixel associatedwith aligned strobe image 232 of FIG. 2D, ambient pixel 522 comprises apixel associated with aligned ambient image 234, and color correctedstrobe pixel 512 comprises a pixel associated with corrected strobeimage data 252. Color corrected strobe pixel 512 may correspond tostrobe pixel 312 in FIG. 3A, and serve as an input to blend function330.

In one embodiment, patch-level correction factors 525 comprise one ormore sets of correction factors for red, green, and blue associated withpatch correction 432 of FIG. 4A, frame-level correction factors 527comprise frame-level correction factors for red, green, and blueassociated with frame-level characterization data 492 of FIG. 4B, andframe-level histogram factors 529 comprise at least a low thresholdintensity and a median threshold intensity for both an ambient histogramand a strobe histogram associated with frame-level characterization data492.

A pixel-level trust estimator 502 computes a pixel-level trust factor503 from strobe pixel 520 and ambient pixel 522. In one embodiment,pixel-level trust factor 503 is computed according to the pseudo-code ofTable 4, where strobe pixel 520 corresponds to strobePixel, ambientpixel 522 corresponds to ambientPixel, and pixel-level trust factor 503corresponds to pixelTrust. Here, ambientPixel and strobePixel maycomprise a vector variable, such as a well-known vec3 or vec4 vectorvariable.

TABLE 4 ambientIntensity = intensity (ambientPixel); strobeIntensity =intensity (strobePixel); stepInput = ambientIntensity * strobeIntensity;pixelTrust = smoothstep (lowEdge, highEdge, stepInput);

Here, an intensity function may implement Equation 1 to computeambientIntensity and strobeIntensity, corresponding respectively to anintensity value for ambientPixel and an intensity value for strobePixel.While the same intensity function is shown computing bothambientIntensity and strobeIntensity, certain embodiments may computeeach intensity value using a different intensity function. A productoperator may be used to compute stepInput, based on ambientIntensity andstrobeIntensity. The well-known smoothstep function implements arelatively smoothly transition from 0.0 to 1.0 as stepInput passesthrough lowEdge and then through highEdge. In one embodiment,lowEdge=0.25 and highEdge=0.66.

A patch-level correction estimator 504 computes patch-level correctionfactors 505 by sampling patch-level correction factors 525. In oneembodiment, patch-level correction estimator 504 implements bilinearsampling over four sets of patch-level color correction samples togenerate sampled patch-level correction factors 505. In an alternativeembodiment, patch-level correction estimator 504 implements distanceweighted sampling over four or more sets of patch-level color correctionsamples to generate sampled patch-level correction factors 505. Inanother alternative embodiment, a set of sampled patch-level correctionfactors 505 is computed using pixels within a region centered aboutstrobe pixel 520. Persons skilled in the art will recognize that anytechnically feasible technique for sampling one or more patch-levelcorrection factors to generate sampled patch-level correction factors505 is within the scope and spirit of the present invention.

In one embodiment, each one of patch-level correction factors 525comprises a red, green, and blue color channel correction factor. In adifferent embodiment, each one of the patch-level correction factors 525comprises a set of line equation parameters for red, green, and bluecolor channels. Each set of line equation parameters may include a slopeand an offset. In another embodiment, each one of the patch-levelcorrection factors 525 comprises a set of quadratic curve parameters forred, green, and blue color channels. Each set of quadratic curveparameters may include a square term coefficient, a linear termcoefficient, and a constant.

In one embodiment, frame-level correction adjustor 506 computes adjustedframe-level correction factors 507 from the frame-level correctionfactors for red, green, and blue according to the pseudo-code of Table5. Here, a mix operator may function according to Equation 2, wherevariable A corresponds to 1.0, variable B corresponds to a correctFramecolor value, and frameTrust may be computed according to an embodimentdescribed below in conjunction with the pseudo-code of Table 6. Asdiscussed previously, correctFrame comprises frame-level correctionfactors. Parameter frameTrust quantifies how trustworthy a particularpair of ambient image and strobe image may be for performing frame-levelcolor correction.

TABLE 5 adjCorrectFrame.r = mix(1.0, correctFrame.r, frameTrust);adjCorrectFrame.g = mix(1.0, correctFrame.g, frameTrust);adjCorrectFrame.b = mix(1.0, correctFrame.b, frameTrust);

When frameTrust approaches zero (correction factors not trustworthy),the adjusted frame-level correction factors 507 converge to 1.0, whichyields no frame-level color correction. When frameTrust is 1.0(completely trustworthy), the adjusted frame-level correction factors507 converge to values calculated previously in Table 3. The pseudo-codeof Table 6 illustrates one technique for calculating frameTrust.

TABLE 6 strobeExp = (WSL*SL + WSM*SM + WSH*SH) / (WSL + WSM + WSH);ambientExp = (WAL*SL + WAM*SM + WAH*SH) / (WAL + WAM + WAH);frameTrustStrobe = smoothstep (SLE, SHE, strobeExp); frameTrustAmbient =smoothstep (ALE, AHE, ambientExp); frameTrust = frameTrustStrobe *frameTrustAmbient;

Here, strobe exposure (strobeExp) and ambient exposure (ambientExp) areeach characterized as a weighted sum of corresponding low thresholdintensity, median threshold intensity, and high threshold intensityvalues. Constants WSL, WSM, and WSH correspond to strobe histogramcontribution weights for low threshold intensity, median thresholdintensity, and high threshold intensity values, respectively. VariablesSL, SM, and SH correspond to strobe histogram low threshold intensity,median threshold intensity, and high threshold intensity values,respectively. Similarly, constants WAL, WAM, and WAH correspond toambient histogram contribution weights for low threshold intensity,median threshold intensity, and high threshold intensity values,respectively; and variables AL, AM, and AH correspond to ambienthistogram low threshold intensity, median threshold intensity, and highthreshold intensity values, respectively. A strobe frame-level trustvalue (frameTrustStrobe) is computed for a strobe frame associated withstrobe pixel 520 to reflect how trustworthy the strobe frame is for thepurpose of frame-level color correction. In one embodiment, WSL=WAL=1.0,WSM=WAM=2.0, and WSH=WAH=0.0. In other embodiments, different weightsmay be applied, for example, to customize the techniques taught hereinto a particular camera apparatus. In certain embodiments, otherpercentile thresholds may be measured, and different combinations ofweighted sums may be used to compute frame-level trust values.

In one embodiment, a smoothstep function with a strobe low edge (SLE)and strobe high edge (SHE) is evaluated based on strobeExp. Similarly, asmoothstep function with ambient low edge (ALE) and ambient high edge(AHE) is evaluated to compute an ambient frame-level trust value(frameTrustAmbient) for an ambient frame associated with ambient pixel522 to reflect how trustworthy the ambient frame is for the purpose offrame-level color correction. In one embodiment, SLE=ALE=0.15, andSHE=AHE=0.30. In other embodiments, different low and high edge valuesmay be used.

In one embodiment, a frame-level trust value (frameTrust) forframe-level color correction is computed as the product offrameTrustStrobe and frameTrustAmbient. When both the strobe frame andthe ambient frame are sufficiently exposed and therefore trustworthyframe-level color references, as indicated by frameTrustStrobe andframeTrustAmbient, the product of frameTrustStrobe and frameTrustAmbientwill reflect a high trust for frame-level color correction. If eitherthe strobe frame or the ambient frame is inadequately exposed to be atrustworthy color reference, then a color correction based on acombination of strobe frame and ambient frame should not be trustworthy,as reflected by a low or zero value for frameTrust.

In an alternative embodiment, the frame-level trust value (frameTrust)is generated according to direct user input, such as via a UI coloradjustment tool having a range of control positions that map to aframeTrust value. The UI color adjustment tool may generate a full rangeof frame-level trust values (0.0 to 1.0) or may generate a valueconstrained to a computed range. In certain settings, the mapping may benon-linear to provide a more natural user experience. In one embodiment,the control position also influences pixel-level trust factor 503(pixelTrust), such as via a direct bias or a blended bias.

A pixel-level correction estimator 508 is configured to generatepixel-level correction factors 509 from sampled patch-level correctionfactors 505, adjusted frame-level correction factors 507, andpixel-level trust factor 503. In one embodiment, pixel-level correctionestimator 508 comprises a mix function, whereby sampled patch-levelcorrection factors 505 is given substantially full mix weight whenpixel-level trust factor 503 is equal to 1.0 and adjusted frame-levelcorrection factors 507 is given substantially full mix weight whenpixel-level trust factor 503 is equal to 0.0. Pixel-level correctionestimator 508 may be implemented according to the pseudo-code of Table7.

TABLE 7 pixCorrection.r = mix(adjCorrectFrame.r, correct.r, pixelTrust);pixCorrection.g= mix(adjCorrectFrame.g, correct.g, pixelTrust);pixCorrection.b = mix(adjCorrectFrame.b, correct.b, pixelTrust);

In another embodiment, line equation parameters comprising slope andoffset define sampled patch-level correction factors 505 and adjustedframe-level correction factors 507. These line equation parameters aremixed within pixel-level correction estimator 508 according topixelTrust to yield pixel-level correction factors 509 comprising lineequation parameters for red, green, and blue channels. In yet anotherembodiment, quadratic parameters define sampled patch-level correctionfactors 505 and adjusted frame-level correction factors 507. In oneembodiment, the quadratic parameters are mixed within pixel-levelcorrection estimator 508 according to pixelTrust to yield pixel-levelcorrection factors 509 comprising quadratic parameters for red, green,and blue channels. In another embodiment, quadratic equations areevaluated separately for frame-level correction factors and patch levelcorrection factors for each color channel, and the results of evaluatingthe quadratic equations are mixed according to pixelTrust.

In certain embodiments, pixelTrust is at least partially computed byimage capture information, such as exposure time or exposure ISO index.For example, if an image was captured with a very long exposure at avery high ISO index, then the image may include significant chromaticnoise and may not represent a good frame-level color reference for colorcorrection.

Pixel-level correction function 510 generates color corrected strobepixel 512 from strobe pixel 520 and pixel-level correction factors 509.In one embodiment, pixel-level correction factors 509 comprisecorrection factors pixCorrection.r, pixCorrection.g, and pixCorrection.band color corrected strobe pixel 512 is computed according to thepseudo-code of Table 8.

TABLE 8 // scale red, green, blue vec3 pixCorrection = (pixCorrection.r,pixCorrection.g, pixCorrection.b); vec3 deNormCorrectedPixel =strobePixel * pixCorrection; normalizeFactor = length(strobePixel) /length(deNormCorrectedPixel); vec3 normCorrectedPixel =deNormCorrectedPixel * normalizeFactor; vec3 correctedPixel =cAttractor(normCorrectedPixel);

Here, pixCorrection comprises a vector of three components (vec3)corresponding pixel-level correction factors pixCorrection.r,pixCorrection.g, and pixCorrection.b. A de-normalized, color correctedpixel is computed as deNormCorrectedPixel. A pixel comprising a red,green, and blue component defines a color vector in a three-dimensionalspace, the color vector having a particular length. The length of acolor vector defined by deNormCorrectedPixel may be different withrespect to a color vector defined by strobePixel. Altering the length ofa color vector changes the intensity of a corresponding pixel. Tomaintain proper intensity for color corrected strobe pixel 512,deNormCorrectedPixel is re-normalized via normalizeFactor, which iscomputed as a ratio of length for a color vector defined by strobePixelto a length for a color vector defined by deNormCorrectedPixel. Colorvector normCorrectedPixel includes pixel-level color correction andre-normalization to maintain proper pixel intensity. A length functionmay be performed using any technically feasible technique, such ascalculating a square root of a sum of squares for individual vectorcomponent lengths.

A chromatic attractor function (cAttractor) gradually converges an inputcolor vector to a target color vector as the input color vectorincreases in length. Below a threshold length, the chromatic attractorfunction returns the input color vector. Above the threshold length, thechromatic attractor function returns an output color vector that isincreasingly convergent on the target color vector. The chromaticattractor function is described in greater detail below in FIG. 5B.

In alternative embodiments, pixel-level correction factors comprise aset of line equation parameters per color channel, with color componentsof strobePixel comprising function inputs for each line equation. Insuch embodiments, pixel-level correction function 510 evaluates the lineequation parameters to generate color corrected strobe pixel 512. Thisevaluation process is illustrated in the pseudo-code of Table 9.

TABLE 9 // evaluate line equation based on strobePixel for red, green,blue vec3 pixSlope = (pixSlope.r, pixSlope.g, pixSlope.b); vec3pixOffset = (pixOffset.r, pixOffset.g, pixOffset.b); vec3deNormCorrectedPixel = (strobePixel * pixSlope) + pixOffset;normalizeFactor = length(strobePixel) / length(deNormCorrectedPixel);vec3 normCorrectedPixel = deNormCorrectedPixel * normalizeFactor; vec3correctedPixel = cAttractor(normCorrectedPixel);

In other embodiments, pixel level correction factors comprise a set ofquadratic parameters per color channel, with color components ofstrobePixel comprising function inputs for each quadratic equation. Insuch embodiments, pixel-level correction function 510 evaluates thequadratic equation parameters to generate color corrected strobe pixel512.

In certain embodiments chromatic attractor function (cAttractor)implements a target color vector of white (1, 1, 1), and causes verybright pixels to converge to white, providing a natural appearance tobright portions of an image. In other embodiments, a target color vectoris computed based on spatial color information, such as an average colorfor a region of pixels surrounding the strobe pixel. In still otherembodiments, a target color vector is computed based on an averageframe-level color. A threshold length associated with the chromaticattractor function may be defined as a constant, or, without limitation,by a user input, a characteristic of a strobe image or an ambient imageor a combination thereof. In an alternative embodiment, pixel-levelcorrection function 510 does not implement the chromatic attractorfunction.

In one embodiment, a trust level is computed for each patch-levelcorrection and applied to generate an adjusted patch-level correctionfactor comprising sampled patch-level correction factors 505. Generatingthe adjusted patch-level correction may be performed according to thetechniques taught herein for generating adjusted frame-level correctionfactors 507.

Other embodiments include two or more levels of spatial color correctionfor a strobe image based on an ambient image, where each level ofspatial color correction may contribute a non-zero weight to a colorcorrected strobe image comprising one or more color corrected strobepixels. Such embodiments may include patches of varying size comprisingvarying shapes of pixel regions without departing the scope of thepresent invention.

FIG. 5B illustrates a chromatic attractor function 560, according to oneembodiment of the present invention. A color vector space is shownhaving a red axis 562, a green axis 564, and a blue axis 566. A unitcube 570 is bounded by an origin at coordinate (0, 0, 0) and an oppositecorner at coordinate (1, 1, 1). A surface 572 having a thresholddistance from the origin is defined within the unit cube. Color vectorshaving a length that is shorter than the threshold distance areconserved by the chromatic attractor function 560. Color vectors havinga length that is longer than the threshold distance are convergedtowards a target color. For example, an input color vector 580 isdefined along a particular path that describes the color of the inputcolor vector 580, and a length that describes the intensity of the colorvector. The distance from the origin to point 582 along input colorvector 580 is equal to the threshold distance. In this example, thetarget color is pure white (1, 1, 1), therefore any additional lengthassociated with input color vector 580 beyond point 582 follows path 584towards the target color of pure white.

One implementation of chromatic attractor function 560, comprising thecAttractor function of Tables 8 and 9 is illustrated in the pseudo-codeof Table 10.

TABLE 10 extraLength = max(length (inputColor), distMin) ; mixValue=(extraLength − distMin) / (distMax− distMin); outputColor = mix(inputColor, targetColor, mixValue);

Here, a length value associated with inputColor is compared to distMin,which represents the threshold distance. If the length value is lessthan distMin, then the “max” operator returns distMin. The mixValue termcalculates a parameterization from 0.0 to 1.0 that corresponds to alength value ranging from the threshold distance to a maximum possiblelength for the color vector, given by the square root of 3.0. IfextraLength is equal to distMin, then mixValue is set equal to 0.0 andoutputColor is set equal to the inputColor by the mix operator.Otherwise, if the length value is greater than distMin, then mixValuerepresents the parameterization, enabling the mix operator toappropriately converge inputColor to targetColor as the length ofinputColor approaches the square root of 3.0. In one embodiment, distMaxis equal to the square root of 3.0 and distMin=1.45. In otherembodiments different values may be used for distMax and distMin. Forexample, if distMin=1.0, then chromatic attractor 560 begins to convergeto targetColor much sooner, and at lower intensities. If distMax is setto a larger number, then an inputPixel may only partially converge ontargetColor, even when inputPixel has a very high intensity. Either ofthese two effects may be beneficial in certain applications.

While the pseudo-code of Table 10 specifies a length function, in otherembodiments, computations may be performed in length-squared space usingconstant squared values with comparable results.

In one embodiment, targetColor is equal to (1,1,1), which representspure white and is an appropriate color to “burn” to in overexposedregions of an image rather than a color dictated solely by colorcorrection. In another embodiment, targetColor is set to a scene averagecolor, which may be arbitrary. In yet another embodiment, targetColor isset to a color determined to be the color of an illumination sourcewithin a given scene.

FIG. 6 is a flow diagram of a method 600 for generating an adjusteddigital photograph, according to one embodiment of the presentinvention. Although the method steps are described in conjunction withthe systems of FIGS. 1A-1D, persons skilled in the art will understandthat any system configured to perform the method steps, in any order, iswithin the scope of the present invention.

Method 600 begins in step 610, where a digital photographic system, suchas digital photographic system 100 of FIG. 1A, receives a triggercommand to take (i.e., capture) a digital photograph. The triggercommand may comprise a user input event, such as a button press, remotecontrol command related to a button press, completion of a timer countdown, an audio indication, or any other technically feasible user inputevent. In one embodiment, the digital photographic system implementsdigital camera 102 of FIG. 1C, and the trigger command is generated whenshutter release button 115 is pressed. In another embodiment, thedigital photographic system implements mobile device 104 of FIG. 1D, andthe trigger command is generated when a UI button is pressed.

In step 612, the digital photographic system samples a strobe image andan ambient image. In one embodiment, the strobe image is taken beforethe ambient image. Alternatively, the ambient image is taken before thestrobe image. In certain embodiments, a white balance operation isperformed on the ambient image. Independently, a white balance operationmay be performed on the strobe image. In other embodiments, such as inscenarios involving raw digital photographs, no white balance operationis applied to either the ambient image or the strobe image.

In step 614, the digital photographic system generates a blended imagefrom the strobe image and the ambient image. In one embodiment, thedigital photographic system generates the blended image according todata flow process 200 of FIG. 2A. In a second embodiment, the digitalphotographic system generates the blended image according to data flowprocess 202 of FIG. 2B. In a third embodiment, the digital photographicsystem generates the blended image according to data flow process 204 ofFIG. 2C. In a fourth embodiment, the digital photographic systemgenerates the blended image according to data flow process 206 of FIG.2D. In each of these embodiments, the strobe image comprises strobeimage 210, the ambient image comprises ambient image 220, and theblended image comprises blended image 280.

In step 616, the digital photographic system presents an adjustment toolconfigured to present at least the blended image, the strobe image, andthe ambient image, according to a transparency blend among two or moreof the images. The transparency blend may be controlled by a userinterface slider. The adjustment tool may be configured to save aparticular blend state of the images as an adjusted image. Theadjustment tool is described in greater detail below in FIGS. 9 and 10.

The method terminates in step 690, where the digital photographic systemsaves at least the adjusted image.

FIG. 7A is a flow diagram of a method 700 for blending a strobe imagewith an ambient image to generate a blended image, according to a firstembodiment of the present invention. Although the method steps aredescribed in conjunction with the systems of FIGS. 1A-1D, personsskilled in the art will understand that any system configured to performthe method steps, in any order, is within the scope of the presentinvention. In one embodiment, method 700 implements data flow 200 ofFIG. 2A. The strobe image and the ambient image each comprise at leastone pixel and may each comprise an equal number of pixels.

The method begins in step 710, where a processor complex within adigital photographic system, such as processor complex 110 withindigital photographic system 100 of FIG. 1A, receives a strobe image andan ambient image, such as strobe image 210 and ambient image 220,respectively. In step 712, the processor complex generates a blendedimage, such as blended image 280, by executing a blend operation 270 onthe strobe image and the ambient image. The method terminates in step790, where the processor complex saves the blended image, for example toNV memory 116, volatile memory 118, or memory system 162.

FIG. 7B is a flow diagram of a method 702 for blending a strobe imagewith an ambient image to generate a blended image, according to a secondembodiment of the present invention. Although the method steps aredescribed in conjunction with the systems of FIGS. 1A-1D, personsskilled in the art will understand that any system configured to performthe method steps, in any order, is within the scope of the presentinvention. In one embodiment, method 702 implements data flow 202 ofFIG. 2B. The strobe image and the ambient image each comprise at leastone pixel and may each comprise an equal number of pixels.

The method begins in step 720, where a processor complex within adigital photographic system, such as processor complex 110 withindigital photographic system 100 of FIG. 1A, receives a strobe image andan ambient image, such as strobe image 210 and ambient image 220,respectively. In step 722, the processor complex generates a colorcorrected strobe image, such as corrected strobe image data 252, byexecuting a frame analysis operation 240 on the strobe image and theambient image and executing and a color correction operation 250 on thestrobe image. In step 724, the processor complex generates a blendedimage, such as blended image 280, by executing a blend operation 270 onthe color corrected strobe image and the ambient image. The methodterminates in step 792, where the processor complex saves the blendedimage, for example to NV memory 116, volatile memory 118, or memorysystem 162.

FIG. 8A is a flow diagram of a method 800 for blending a strobe imagewith an ambient image to generate a blended image, according to a thirdembodiment of the present invention. Although the method steps aredescribed in conjunction with the systems of FIGS. 1A-1D, personsskilled in the art will understand that any system configured to performthe method steps, in any order, is within the scope of the presentinvention. In one embodiment, method 800 implements data flow 204 ofFIG. 2C. The strobe image and the ambient image each comprise at leastone pixel and may each comprise an equal number of pixels.

The method begins in step 810, where a processor complex within adigital photographic system, such as processor complex 110 withindigital photographic system 100 of FIG. 1A, receives a strobe image andan ambient image, such as strobe image 210 and ambient image 220,respectively. In step 812, the processor complex estimates a motiontransform between the strobe image and the ambient image. In step 814,the processor complex renders at least an aligned strobe image or analigned ambient image based the estimated motion transform. In certainembodiments, the processor complex renders both the aligned strobe imageand the aligned ambient image based on the motion transform. The alignedstrobe image and the aligned ambient image may be rendered to the sameresolution so that each is aligned to the other. In one embodiment,steps 812 and 814 together comprise alignment operation 230. In step816, the processor complex generates a blended image, such as blendedimage 280, by executing a blend operation 270 on the aligned strobeimage and the aligned ambient image. The method terminates in step 890,where the processor complex saves the blended image, for example to NVmemory 116, volatile memory 118, or memory system 162.

FIG. 8B is a flow diagram of a method 802 for blending a strobe imagewith an ambient image to generate a blended image, according to a fourthembodiment of the present invention. Although the method steps aredescribed in conjunction with the systems of FIGS. 1A-1D, personsskilled in the art will understand that any system configured to performthe method steps, in any order, is within the scope of the presentinvention. In one embodiment, method 802 implements data flow 206 ofFIG. 2D. The strobe image and the ambient image each comprise at leastone pixel and may each comprise an equal number of pixels.

The method begins in step 830, where a processor complex within adigital photographic system, such as processor complex 110 withindigital photographic system 100 of FIG. 1A, receives a strobe image andan ambient image, such as strobe image 210 and ambient image 220,respectively. In step 832, the processor complex estimates a motiontransform between the strobe image and the ambient image. In step 834,the processor complex may render at least an aligned strobe image or analigned ambient image based the estimated motion transform. In certainembodiments, the processor complex renders both the aligned strobe imageand the aligned ambient image based on the motion transform. The alignedstrobe image and the aligned ambient image may be rendered to the sameresolution so that each is aligned to the other. In one embodiment,steps 832 and 834 together comprise alignment operation 230.

In step 836, the processor complex generates a color corrected strobeimage, such as corrected strobe image data 252, by executing a frameanalysis operation 240 on the aligned strobe image and the alignedambient image and executing a color correction operation 250 on thealigned strobe image. In step 838, the processor complex generates ablended image, such as blended image 280, by executing a blend operation270 on the color corrected strobe image and the aligned ambient image.The method terminates in step 892, where the processor complex saves theblended image, for example to NV memory 116, volatile memory 118, ormemory system 162.

While the techniques taught herein are discussed above in the context ofgenerating a digital photograph having a natural appearance from anunderlying strobe image and ambient image with potentially discordantcolor, these techniques may be applied in other usage models as well.

For example, when compositing individual images to form a panoramicimage, color inconsistency between two adjacent images can create avisible seam, which detracts from overall image quality. Persons skilledin the art will recognize that frame analysis operation 240 may be usedin conjunction with color correction operation 250 to generatedpanoramic images with color-consistent seams, which serve to improveoverall image quality. In another example, frame analysis operation 240may be used in conjunction with color correction operation 250 toimprove color consistency within high dynamic range (HDR) images.

In yet another example, multispectral imaging may be improved byenabling the addition of a strobe illuminator, while maintainingspectral consistency. Multispectral imaging refers to imaging ofmultiple, arbitrary wavelength ranges, rather than just conventionalred, green, and blue ranges. By applying the above techniques, amultispectral image may be generated by blending two or moremultispectral images having different illumination sources, i.e.,different lighting conditions.

In still other examples, the techniques taught herein may be applied inan apparatus that is separate from digital photographic system 100 ofFIG. 1A. Here, digital photographic system 100 may be used to generateand store a strobe image and an ambient image. The strobe image andambient image are then combined later within a computer system, disposedlocally with a user, or remotely within a cloud-based computer system.In one embodiment, method 802 comprises a software module operable withan image processing tool to enable a user to read the strobe image andthe ambient image previously stored, and to generate a blended imagewithin a computer system that is distinct from digital photographicsystem 100.

Persons skilled in the art will recognize that while certainintermediate image data may be discussed in terms of a particular imageor image data, these images serve as illustrative abstractions. Suchbuffers may be allocated in certain implementations, while in otherimplementations intermediate data is only stored as needed. For example,aligned strobe image 232 may be rendered to completion in an allocatedimage buffer during a certain processing step or steps, oralternatively, pixels associated with an abstraction of an aligned imagemay be rendered as needed without a need to allocate an image buffer tostore aligned strobe image 232.

While the techniques described above discuss color correction operation250 in conjunction with a strobe image that is being corrected based onan ambient reference image, a strobe image may serve as a referenceimage for correcting an ambient image. In one embodiment ambient image220 is subjected to color correction operation 250, and blend operation270 operates as previously discussed for blending an ambient image and astrobe image.

User Interface Elements

FIG. 9 illustrates a user interface (UI) system 900 for generating acombined image 920, according to one embodiment of the presentinvention. Combined image 920 comprises a combination of at least tworelated images. In one embodiment, combined image 920 comprises an imagerendering that combines an ambient image, a strobe image, and a blendedimage. The strobe image may comprise a color corrected strobe image. Forexample combined image 920 may include a rendering that combines ambientimage 220, strobe image 210, and blended image 280 of FIGS. 2A-2D. Inone configuration, combined image 920 comprises an image rendering thatcombines an ambient image and a blended image. In another configuration,combined image 920 comprises an image rendering that combines an ambientimage and a strobe image.

In one embodiment, UI system 900 presents a display image 910 thatincludes, without limitation, combined image 920, a UI control grip 930comprising a continuous linear position UI control element configured tomove along track 932, and two or more anchor points 940, which may eachinclude a visual marker displayed within display image 910. Inalternative embodiments, UI control grip 930 may comprise a continuousrotational position UI control element, or any other technicallyfeasible continuous position UI control element. In certain embodiments,UI control grip 930 is configured to indicated a current setting for aninput parameter, whereby the input parameter may be changed by a uservia a tap gesture or a touch and drag gesture. The tap gesture may beused to select a particular position of UI control grip 930, while atouch and drag gesture may be used to enter a sequence of positions forUI control grip 930.

In one embodiment, UI system 900 is generated by an adjustment toolexecuting within processor complex 110 and display image 910 isdisplayed on display unit 112. The at least two component images mayreside within NV memory 116, volatile memory 118, memory subsystem 162,or any combination thereof. In another embodiment, UI system 900 isgenerated by an adjustment tool executing within a computer system, suchas a laptop computer, desktop computer, server computer, or any othertechnically feasible computer system. The at least two component imagesmay be transmitted to the computer system or may be generated by anattached camera device. In yet another embodiment, UI system 900 isgenerated by a cloud-based server computer system, which may downloadthe at least two component images to a client browser, which may executecombining operations described below.

UI control grip 930 is configured to move between two end points,corresponding to anchor points 940-A and 940-B. One or more anchorpoints, such as anchor point 940-S may be positioned between the two endpoints. Each anchor point 940 should be associated with a specificimage, which may be displayed as combined image 920 when UI control grip930 is positioned directly over the anchor point.

In one embodiment, anchor point 940-A is associated with the ambientimage, anchor point 940-S is associated with the strobe image, andanchor point 940-B is associated with the blended image. When UI controlgrip 930 is positioned at anchor point 940-A, the ambient image isdisplayed as combined image 920. When UI control grip 930 is positionedat anchor point 940-S, the strobe image is displayed as combined image920. When UI control grip 930 is positioned at anchor point 940-B, theblended image is displayed as combined image 920. In general, when UIcontrol grip 930 is positioned between anchor points 940-A and 940-S,inclusive, a first mix weight is calculated for the ambient image andthe strobe image. The first mix weight may be calculated as having avalue of 0.0 when the UI control grip 930 is at anchor point 940-A and avalue of 1.0 when UI control grip 930 is at anchor point 940-S. A mixoperation, described previously, is then applied to the ambient imageand the strobe image, whereby a first mix weight of 0.0 gives completemix weight to the ambient image and a first mix weight of 1.0 givescomplete mix weight to the strobe image. In this way, a user may blendbetween the ambient image and the strobe image. Similarly, when UIcontrol grip 930 is positioned between anchor point 940-S and 940-B,inclusive, a second mix weight may be calculated as having a value of0.0 when UI control grip 930 is at anchor point 940-S and a value of 1.0when UI control grip 930 is at anchor point 940-B. A mix operation isthen applied to the strobe image and the blended image, whereby a secondmix weight of 0.0 gives complete mix weight to the strobe image and asecond mix weight of 1.0 gives complete mix weight to the blended image.

This system of mix weights and mix operations provide a UI tool forviewing the ambient image, strobe image, and blended image as a gradualprogression from the ambient image to the blended image. In oneembodiment, a user may save a combined image 920 corresponding to anarbitrary position of UI control grip 930. The adjustment toolimplementing UI system 900 may receive a command to save the combinedimage 920 via any technically feasible gesture or technique. Forexample, the adjustment tool may be configured to save combined image920 when a user gestures within the area occupied by combined image 920.Alternatively, the adjustment tool may save combined image 920 when auser presses, but does not otherwise move UI control grip 930. Inanother implementation, the adjustment tool may save combined image 920when the user enters a gesture, such as pressing a save button 931,dedicated to receive a save command.

In one embodiment, save button 931 is displayed and tracks the positionof UI control grip 930 while the user adjusts UI control grip 930. Theuser may click save button 931 at any time to save an imagecorresponding to the current position of UI control grip 930.

In another embodiment, save button 931 is displayed above (or inproximity to) UI control grip 930, when the user does not have theirfinger on UI control grip 930. If the user touches the save button 931,an image is saved corresponding to the position of UI control grip 930.If the user subsequently touches the UI control grip 930, then savebutton 931 disappears. In one usage case, a user adjusts the UI controlgrip 930, lifts their finger from the UI control grip, and save button931 is displayed conveniently located above UI control grip 930. Theuser may then save a first adjusted image corresponding to this firstposition of UI control grip 930. The user then makes a second adjustmentusing UI control grip 930. After making the second adjustment, the userlifts their finger from UI control grip 930 and save button 931 is againdisplayed above the current position of UI control grip 930. The usermay save a second adjusted image, corresponding to a second UI controlgrip position, by pressing save button 931 again.

In certain embodiments, UI control grip 930 may be positioned initiallyin a default position, or initially in a calculated position, such ascalculated from current image data or previously selected positioninformation. The user may override the initial position by moving UIcontrol grip 930. The initial position may be indicated via an initialposition marker 933 disposed along track 932 to assist the user inreturning to the initial position after moving UI control grip 930 awayfrom the initial position. In one embodiment, UI control grip 930 isconfigured to return to the initial position when a user taps in closeproximity to initial position marker 933. In certain embodiments, theinitial position marker may be configured to change color or intensitywhen UI control grip 930 is positioned in close proximity to the initialposition marker.

In certain embodiments, the adjustment tool provides a continuousposition UI control, such as UI control grip 930, for adjustingotherwise automatically generated parameter values. For example, acontinuous UI control may be configured to adjust, without limitation, aframeTrust value, a bias or function applied to a plurality ofindividual pixelTrust values, blend surface parameters such as one ormore of heights 355-358 illustrated in FIG. 3C, blend surface curvatureas illustrated in FIG. 3D, or any combination thereof. In oneembodiment, an initial parameter value is calculated and mapped to acorresponding initial position for UI control grip 930. The user maysubsequently adjust the parameter value via UI control grip 930. Anytechnically feasible mapping between a position for UI control grip 930and the corresponding value may be implemented without departing thescope and spirit of the present invention.

Persons skilled in the art will recognize that the above system of mixweights and mix operations may be generalized to include two or moreanchor points, which may be associated with two or more related imageswithout departing the scope and spirit of the present invention. Suchrelated images may comprise, without limitation, an ambient image and astrobe image, two ambient images having different exposure and a strobeimage, or two or more ambient images having different exposure.

Furthermore, a different continuous position UI control, such as arotating knob, may be implemented rather than UI control grip 930. Incertain embodiments, a left-most anchor point corresponds to an ambientimage, a mid-point anchor point corresponds to a blended image, and aright-most anchor point corresponds to a strobe image.

FIG. 10A is a flow diagram of a method 1000 for generating a combinedimage, according to one embodiment of the present invention. Althoughthe method steps are described in conjunction with the systems of FIGS.1A-1D, persons skilled in the art will understand that any systemconfigured to perform the method steps, in any order, is within thescope of the present invention.

Method 1000 begins in step 1010, where an adjustment tool executingwithin a processor complex, such as processor complex 110, loads atleast two related source images. In step 1012, the adjustment toolinitializes a position for a UI control, such as UI control grip 930 ofFIG. 9, to an initial position. In one embodiment, the initial UIcontrol position corresponds to an anchor point, such as anchor point940-A, anchor point 940-S, or anchor point 940-B. In another embodiment,the initial UI control position corresponds to a recommended UI controlposition. In certain embodiments, the recommended UI control position isbased on previous UI control positions associated with a specific UIevent that serves to indicate user acceptance of a resulting image, suchas a UI event related to saving or sharing an image based on aparticular UI control position. For example, the recommended UI controlposition may represent an historic average of previous UI controlpositions associated with the UI event. In another example, therecommended UI control position represents a most likely value from ahistogram of previous UI control positions associated with the UI event.

In certain embodiments, the recommended UI control position is based onone or more of the at least two related source images. For example, arecommended UI control position may be computed to substantiallyoptimize a certain cost function associated with a combined image 920.The cost function may assign a cost to over-exposed regions and anothercost to under-exposed regions of a combined image associated with aparticular UI control position. Optimizing the cost function may thencomprise rendering combined images having different UI control positionsto find a UI control position that substantially minimizes the costfunction over each rendered combined image. The combined images may berendered at full resolution or reduced resolution for calculating arespective cost function. The cost function may assign greater cost toover-exposed regions than under-exposed regions to prioritize reducingover-exposed areas. Alternatively, the cost function may assign greatercost to under-exposed regions than over-exposed regions to prioritizereducing under-exposed areas. One exemplary technique for calculating arecommended UI control position for UI control grip 930 is illustratedin greater detail below in FIG. 10B.

In certain alternative embodiments, the cost function is computedwithout rendering a combined image. Instead, the cost function for agiven UI control position is computed via interpolating or otherwisecombining one or more attributes for each image associated with adifferent anchor point. For example, a low intensity mark computed at afifteenth percentile point for each of two different images associatedwith corresponding anchor points may comprise one of two attributesassociated with the two different images. A second attribute maycomprise a high intensity mark, computed at an eighty-fifth percentilemark. One exemplary cost function defines a combined low intensity markas a mix of two different low intensity marks corresponding to each oftwo images associated with two different anchor points, and a highintensity mark as a mix of two different high intensity markscorresponding to each of the two images. The cost function value is thendefined as the sum of an absolute distance from the combined lowintensity mark and a half intensity value and an absolute distance fromthe combined high intensity mark and a half intensity value.Alternatively, each distance function may be computed from a mix ofmedian values for each of the two images. Persons skilled in the artwill recognize that other cost functions may be similarly implementedwithout departing the scope and spirit of the present invention.

In one embodiment, computing the recommended UI control positionincludes adding an offset estimate, based on previous user offsetpreferences expressed as a history of UI control position overrides.Here, the recommended UI control position attempts to model differencesin user preference compared to a recommended UI control positionotherwise computed by a selected cost function. In one implementation,the offset estimate is computed along with an offset weight. As offsetsamples are accumulated, the offset weight may increase, therebyincreasing the influence of the offset estimate on a final recommendedUI control position. Each offset sample may comprise a differencebetween a recommended UI control position and a selected UI controlposition expressed as a user override of the recommended UI controlposition. As the offset weight increases with accumulating samples, therecommended UI control position may gradually converge with a userpreference of UI control position. The goal of the above technique is toreduce an overall amount and frequency of override intervention by theuser by generating recommended UI control positions that are moreconsistent with a preference demonstrated by for the user.

In step 1014, the adjustment tool displays a combined image, such ascombined image 920, based on a position of the UI control and the atleast two related source images. Any technically feasible technique maybe implemented to generate the combined image. In one embodiment, step1014 includes generating the combined image, whereby generatingcomprises mixing the at least two related source images as describedpreviously in FIG. 9. In certain embodiments, the adjustment tooldisplays a “save” button, when the user is not touching the UI control.In certain other embodiments, the adjustment tool displays the savebutton regardless of whether the user is touching the UI control.

In step 1016, the adjustment tool receives user input. The user inputmay include, without limitation, a UI gesture such as a selectiongesture or click gesture within display image 910. If, in step 1020, theuser input should trigger a display update, then the method proceedsback to step 1014. A display update may include any change to displayimage 910. As such, a display update may include, without limitation, achance in position of the UI control, an updated rendering of combinedimage 920, or a change in visibility of a given UI element, such as savebutton 931. Otherwise, the method proceeds to step 1030.

If, in step 1030, the user input does not comprise a command to exit,then the method proceeds to step 1032, where the adjustment toolperforms a command associated with the user input. In one embodiment,the command comprises a save command and the adjustment tool then savesthe combined image, which is generated according to a current positionof the UI control. The method then proceeds back to step 1016.

Returning to step 1030, if the user input comprises a command to exit,then the method terminates in step 1035, and the adjustment tool exits,thereby terminating execution.

In one embodiment, one of the two related images is an ambient image,while another of the two related images is a strobe image. In certainembodiments, the strobe image comprises a color corrected strobe image.

FIG. 10B is a flow diagram of a method 1002 for calculating arecommended UI control position for blending two different images,according to one embodiment of the present invention. Although themethod steps are described in conjunction with the systems of FIGS.1A-1D, persons skilled in the art will understand that any systemconfigured to perform the method steps, in any order, is within thescope of the present invention. In one embodiment, the control positioncorresponds to a UI control position such as a position for UI controlgrip 930, used to generate blending weights for two or more relatedimages.

The two different images may include regions having different exposureand lighting characteristics. For example, a strobe image may includeexcessively bright or saturated regions where the strobe reflectedalmost fully, while an ambient image may not include saturated regions,but may instead have inadequately illuminated regions.

A combined image, as described above, may include an excessively brightregion as a consequence of one of the two different images having anoverexposed region, or an inadequately exposed region as a consequenceof one of the two different images having an inadequately exposedregion. In one embodiment, a combined image is generated by mixing thetwo different images according to a mix weight. For certain pairs of twodifferent images, reducing the mix weight of a first image may improveimage quality by reducing the influence of overexposed regions withinthe first image. Similarly, reducing the mix weight of a second imagemay improve image quality by reducing the influence of inadequatelyexposed regions in the second image. In certain scenarios, a balancedmix weight between the first image and the second image may produce goodimage quality by reducing the influence of excessively bright regions inthe first image while also reducing the influence of inadequatelyexposed regions in the second image. Method 1002 iteratively finds a mixweight that optimizes a cost function that is correlated to imagequality of the combined image.

Method 1002 begins is step 1050, where a selection function selects aninitial blend weight. In one embodiment, the selection function isassociated with the adjustment tool of FIG. 10A. The initial blendweight may give complete weight to the first image and no weight to thesecond image, so that the combined image is equivalent to the firstimage. Alternatively, the initial blend weight may give complete weightto the second image, so that the combined image is equivalent to thesecond image. In practice, any technically feasible initial blend weightmay also be implemented. In step 1052, the selection function renders acombined image according to a current blend weight, based on the firstimage and the second image. Initially, the current blend weight shouldbe the initial blend weight.

In step 1054, the selection function computes a cost function value forthe combined image. In one embodiment, the cost function is proportionalto image area that is either overexposed or underexposed. A larger costfunction value indicates more overexposed or underexposed area; suchoverexposed or underexposed areas are correlated to lower image qualityfor the combined image. In one exemplary implementation, the costfunction comprises a sum where each pixel within the combined image addsa constant value to the cost function if the pixel intensity is below alow threshold (underexposed) or above a high threshold (overexposed). Inanother exemplary implementation, the cost function comprises a sumwhere each pixel adds an increasing value to the cost function inproportion to overexposure or underexposure. In other words, as thepixel increases intensity above the high threshold, the pixel adds anincreasing cost to the cost function; similarly, as the pixel decreasesintensity below the low threshold, the pixel adds an increasing cost tothe cost function. In one embodiment, the high threshold is 90% ofmaximum defined intensity for the pixel and the low threshold is 10% ofthe maximum defined intensity for the pixel. Another exemplary costfunction implements an increasing cost proportional to pixel intensitydistance from a median intensity for the combined image. Yet anotherexemplary cost function combines two or more cost components, such aspixel intensity distance from the median intensity for the combinedimage and incremental cost for pixel intensity values above the highthreshold or below the low threshold, where each cost component may bescaled according to a different weight.

In one embodiment, the cost function includes a repulsion cost componentthat increases as the control position approaches a specified anchorpoint. In one exemplary implementation, the repulsion cost component maybe zero unless the control position is less than a threshold distance tothe anchor point. When the control position is less than the thresholddistance to the anchor point, the repulsion cost component increasesaccording to any technically feasible function, such as a linear,logarithmic, or exponential function. The repulsion cost componentserves to nudge the recommended UI control position away from thespecified anchor point. For example, the repulsion cost component mayserve to nudge the recommended UI control position away from extremecontrol position settings, such as away from anchor points 940-A and940-B. In certain embodiments, the cost function may include anattraction cost component that decreases as the control positionapproaches a specified anchor point. The attraction cost component mayserve to slightly favor certain anchor points.

If, in step 1060 searching for a recommended UI control position is notdone, then the method proceeds to step 1062, where the selectionfunction selects a next blend weight to be the current blend weight.Selecting a next blend weight may comprise linearly sweeping a range ofpossible blend weights, performing a binary search over the range ofpossible blend weights, or any other technically feasible search orderfor blend weights. In general, two different images should not have amonotonic cost function over the range of possible blend weights,however, the cost function may have one global minimum that may bediscovered via a linear sweep or a binary search that identifies andrefines a bounding region around the global minimum.

Returning to step 1060, if searching for a recommended UI controlposition is done, then the method proceeds to step 1070. Here arecommended UI control position corresponds to a blend weight thatyields a rendered combined image having a minimum cost function over therange of possible blend weights. In step 1070, the selection functioncauses a UI control position to correspond to a best cost functionvalue. For example, the selection tool may return a parametercorresponding to a recommended UI control position, thereby causing theadjustment tool to move UI control grip 930 to a position correspondingto the recommended UI control position. The method terminates in step1090.

Method 1002 may be practiced over multiple images and multiple blendranges. For example, the recommended UI control position may represent ablend weight from a set of possible blend ranges associated with thefull travel range of UI control grip 930 over multiple anchor points,each corresponding to a different image. As shown in FIG. 9, threeimages are represented by anchor points 940, and two different blendranges are available to blend two adjacent images. Persons skilled inthe art will recognize that embodiments of the present invention may bepracticed over an arbitrary set of images, including ambient images,strobe images, color corrected strobe images, and blended images.

FIGS. 11A-11C illustrate a user interface configured to adapt to deviceorientation while preserving proximity of a user interface controlelement to a hand grip edge, according to embodiments of the presentinvention. The user interface comprises a display object 1120, such ascombined image 920 of FIG. 9, and a UI control 1132, which may compriseUI control grip 930 and track 932. Both display object 1120 and UIcontrol 1132 are displayed on display screen 1112, which resides withinmobile device 1110. A hand grip edge 1130 represents a portion of mobiledevice 1110 being held by a user. As shown, when the user rotates mobiledevice 1110, the display object responds by rotating to preserve a UI uporientation that is consistent with a user's sense of up and down;however, UI control 1132 remains disposed along user grip edge 1130,thereby preserving the user's ability to reach UI control 1132, such asto enter gestures. FIG. 11A illustrates mobile device 1110 in a typicalup right position. As shown, hand grip edge 1130 is at the base ofmobile device 1110. FIG. 11B illustrates mobile device 1110 in a typicalupside down position. As shown, hand grip edge 1130 is at the top ofmobile device 1110. FIG. 11C illustrates mobile device 1110 in asideways position. As shown, hand grip edge 1130 is on the side ofmobile device 1110.

In one embodiment, a UI up orientation is determined by gravitationalforce measurements provided by an accelerometer (force detector)integrated within mobile device 1110. In certain embodiments, hand gripedge 1130 is presumed to be the same edge of the device, whereby a useris presumed to not change their grip on mobile device 1110. However, incertain scenarios, a user may change their grip, which is then detectedby a hand grip sensor implemented in certain embodiments, as illustratedbelow in FIG. 11D. For example, when a user grips mobile device 1110,hand grip sensors detect the user grip, such as via a capacitive sensor,to indicate a hand grip edge 1130. When the user changes their grip, adifferent hand grip edge 1130 may be detected.

FIG. 11D illustrates a mobile device incorporating grip sensors 1142,1144, 1146, 1148 configured to detect a user grip, according to oneembodiment of the present invention. As shown, grip sensor 1142 isdisposed at the left of mobile device 1110, grip sensor 1144 is disposedat the bottom of the mobile device, grip sensor 1146 is disposed at theright of the mobile device, and grip sensor 1148 is disposed at the topof the mobile device. When a user grips mobile device 1110 from aparticular edge, a corresponding grip sensor indicates to mobile device1110 which edge is being gripped by the user. For example, if a usergrips the bottom of mobile device 1110 along grip sensor 1144, then UIcontrol 1132 is positioned along the corresponding edge, as shown. Inone embodiment, grip sensors 1142-1148 each comprise an independentcapacitive touch detector.

In certain scenarios, a user may grip mobile device 1110 using two handsrather than just one hand. In such scenarios, two or more grip sensorsmay simultaneously indicate a grip. Furthermore, the user may alternatewhich hand is gripping the mobile device, so that one or more of thegrip sensors 1142-1148 alternately indicate a grip. In the abovescenarios, when a grip sensor 1142-1148 indicates that the user changedtheir grip position to a new grip location, the new grip location mayneed to be held by the user for a specified time interval before the UIcontrol is reconfigured according to the new grip position. In otherwords, selecting a new grip position may require overcoming a hysteresisfunction based on a hold time threshold. In each case, the UI uporientation may be determined independently according to one or moregravitational force measurements.

In one embodiment, two or more light-emitting diode (LED) illuminatorsare disposed on the back side of mobile device 1110. Each of the two ormore LED illuminators is associated with a device enclosure regioncorresponding to a grip sensor. When a given grip sensor indicates agrip presence, a corresponding LED is not selected as a photographicilluminator for mobile device 1110. One or more different LEDs may beselected to illuminate a subject being photographed by mobile device1110.

FIG. 11E is a flow diagram of a method 1100 for orienting a userinterface surface with respect to a control element, according to oneembodiment of the present invention. Although the method steps aredescribed in conjunction with the systems of FIGS. 1A-1D, personsskilled in the art will understand that any system configured to performthe method steps, in any order, is within the scope of the presentinvention.

Method 1100 begins in step 1160, where a window manager executing withina computing device, such as mobile device 1110 of FIG. 11A, initializesa user interface (UI) comprising display object 1120 and UI control1132. In step 1162, the window manager receives an update event, such asa user input event. In step 1164, the window manager determines a gripposition where a user is likely holding the mobile device 1110. Forexample, the window manager may determine the grip position based on anassumption that the user will hold the mobile device along a consistentedge. The consistent edge may be initially determined, for example, asthe edge closest to a physical button or UI button pressed by the user.Alternatively, the window manager may determine the grip position basedon input data from one or more grip sensors, such as grip sensors 1142,1144, 1146, and 1148. In step 1166, the window manager determines an upposition. For example, the window manage may determine an up positionbased on a gravity force vector reported by an accelerometer. If, instep 1170 the window manager determines that a change to a current UIconfiguration in needed, then the method proceeds to step 1172.Otherwise the method proceeds back to step 1162. A change to the UIconfiguration may be needed, without limitation, if a new up orientationis detected or a new grip position is detected. In step 1172, the windowmanager updates the UI configuration to reflect a new grip position or anew up orientation, or a combination thereof. A new UI configurationshould position UI control 1132 along the side of mobile device 1110corresponding to a user grip. In one embodiment, of the user is grippingmobile device 1110 along two edges, then UI control 1132 may bepositioned corresponding to the edge closest to being in a downorientation. Alternatively, the UI control 1132 may be positionedcorresponding to a right hand preference or a left hand preference. Aright or left hand preference may be selected by the user, for exampleas a control panel option.

If, in step 1180, the method should not terminate, then the methodproceeds back to step 1162. Otherwise, the method terminates in step1190.

In one embodiment the window manager comprises a system facilityresponsible for generating a window presentation paradigm. In otherembodiments, the window manager comprises a set of window managementfunctions associated with a given application or software module.

FIG. 12A illustrates a user interface (UI) control selector 1210configured to select one active control 1214 from one or more availablecontrols 1212, 1214, 1216, according to embodiments of the presentinvention. The one or more available controls 1212, 1214, 1216 areconceptually organized as a drum that may be rotated up or down inrepose to a corresponding rotate up gesture or rotate down gesture. Acontrol aperture 1218 represents a region in which active control 1214may operate. As shown, active control 1214 is a linear slider control,which may be used to input a particular application parameter. Control1216 is shown as being not active, but may be made active by rotatingthe drum down using a rotate down gesture to expose control 1216 withincontrol aperture 1218. Similarly, control 1212 may be made active byrotating the drum up using rotate up gesture. Inactive controls 1212,1216 may be displayed as being partially obscured or partiallytransparent as an indication to the user that they are available.

In one embodiment, the rotate up gesture is implemented as a two-fingertouch and upward swipe gesture, illustrated herein as rotate up gesture1220. Similarly, the rotate down gesture is implemented as a two-fingertouch and downward swipe gesture, illustrated herein as rotate downgesture 1222. In an alternative embodiment, the rotate up gesture isimplemented as a single touch upward swipe gesture within controlselection region 1224 and the rotate down gesture is implemented as asingle touch downward swipe gesture within control selection region1224.

Motion of the drum may emulate physical motion and include propertiessuch as rotational velocity, momentum, and frictional damping. Alocation affinity function may be used to snap a given control intovertically centered alignment within control aperture 1218. Personsskilled in the art will recognize that any motion simulation scheme maybe implemented to emulate drum motion without departing the scope andspirit of the present invention.

FIG. 12B illustrates a user interface control selector 1230 configuredto select one active control 1234 from one or more available controls1232, 1234, 1236, according to embodiments of the present invention. Theone or more available controls 1232, 1234, 1236 are conceptuallyorganized as a flat sheet that may be slid up or slide down in repose toa corresponding slide up gesture or slide down gesture. A controlaperture 1238 represents a region in which active control 1234 mayoperate. As shown, active control 1234 is a linear slider control, whichmay be used to input a particular application parameter. Control 1236 isshown as being not active, but may be made active by siding the sheetdown using the slide down gesture to expose control 1236 within controlaperture 1238. Similarly, control 1232 may be made active by sliding thesheet up using the slide up gesture. Inactive controls 1232, 1236 may bedisplayed as being partially obscured or partially transparent as anindication to the user that they are available.

In one embodiment, the slide up gesture is implemented as a two-fingertouch and upward swipe gesture, illustrated herein as slide up gesture1240. Similarly, the slide down gesture is implemented as a two-fingertouch and downward swipe gesture, illustrated herein as slide downgesture 1242. In an alternative embodiment, the slide up gesture isimplemented as a single touch upward swipe gesture within controlselection region 1244 and the slide down gesture is implemented as asingle touch downward swipe gesture within control selection region 1244

Motion of the sheet may emulate physical motion and include propertiessuch as velocity, momentum, and frictional damping. A location affinityfunction may be used to snap a given control into vertically centeredalignment within control aperture 1238. Persons skilled in the art willrecognize that any motion simulation scheme may be implemented toemulate sheet motion without departing the scope and spirit of thepresent invention.

Active control 1214 and active control 1234 may each comprise anytechnically feasible UI control or controls, including, withoutlimitation, any continuous control, such as a slider bar, or any type ofdiscrete control, such as a set of one or more buttons. In oneembodiment, two or more active controls are presented within controlaperture 1218, 1238.

More generally, in FIGS. 12A and 12B, one or more active controls aredistinguished from available controls that are not currently active. Anytechnically feasible technique may be implemented to distinguish the oneor more active controls from available controls that are not currentlyactive. For example, the one or more active controls may be rendered ina different color or degree of opacity; the one or more active controlsmay be rendered using thicker lines or bolder text, or any other visiblydistinctive feature.

FIG. 12C is a flow diagram a method 1200 for selecting an active controlfrom one or more available controls, according to one embodiment of thepresent invention. Although the method steps are described inconjunction with the systems of FIGS. 1A-1D, persons skilled in the artwill understand that any system configured to perform the method steps,in any order, is within the scope of the present invention.

Method 1200 begins in step 1250, where an application configures a UIcontrol selector to include at least two different UI controls.Configuration may be performed via one or more API calls associated witha window manager, for example via an object registration mechanism thatregisters each UI control and related settings with the UI controlselector. One of the at least two different UI controls may be selectedinitially as an active control.

In step 1252, the UI control selector enables the active control,allowing the active control to receive user input. In step 1254, thewindow manager receives an input event. The input event may comprise auser input event targeting the active control, a user input eventtargeting the UI control selector, or any other technically feasibleevent, including a terminate signal. If, in step 1260, the input eventcomprises an active control input, then the method proceeds to step1262, where the active control receives the input event and transmits acorresponding action based on the event to the application. In oneembodiment, the application is configured to receive actions resultingfrom either of the at least two different UI controls. In certainembodiments, the application is configured to receive actions from anyof the at least two different UI controls, although only the activecontrol may actually generate actions in any one configuration of the UIcontrol selector. Upon completing step 1262, the method proceeds back tostep 1254.

Returning to step 1260, if the input event does not comprise an activecontrol input, then the method proceeds to step 1270. If, in step 1270the input event comprises an event to select a different control as theactive control, then the method proceeds to step 1272, where the UIcontrol selector changes which control is the active control. Uponcompleting step 1272, the method proceeds back to step 1252.

Returning to step 1270, if the input event does not comprise an event toselect a different control, then the method proceeds to step 1280. If,in step 1280, the input event comprises a signal to exit then the methodterminates in step 1290, otherwise, the method proceeds back to step1252.

In one embodiment the window manager comprises a system facilityresponsible for generating a window presentation paradigm. In otherembodiments, the window manager comprises a set of window managementfunctions associated with a given application or software module.

FIG. 13A illustrates a data flow process 1300 for selecting an ambienttarget exposure coordinate, according to one embodiment of the presentinvention. An exposure coordinate is defined herein as a coordinatewithin a two-dimensional image that identifies a representative portionof the image for computing exposure for the image. The goal of data flowprocess 1300 is to select an exposure coordinate used to establishexposure for sampling an ambient image. The ambient image will then becombined with a related strobe image. Because the strobe image maybetter expose certain portions of a scene being photographed, thoseportions may be assigned reduced weight when computing ambient exposure.Here, the ambient target exposure coordinate conveys an exposure targetto a camera subsystem, which may then adjust sensitivity, exposure time,aperture, or any combination thereof to generate mid-tone intensityvalues at the ambient target exposure coordinate in a subsequentlysampled ambient image.

An evaluation strobe image 1310 is sampled based on at least a firstevaluation exposure coordinate. An evaluation ambient image 1213 isseparately sampled based on the at least a second evaluation exposurecoordinate. In one embodiment, the second evaluation exposure coordinatecomprises the first evaluation exposure coordinate. A strobe influencefunction 1320 scans the evaluation strobe image 1310 and the evaluationambient image 1312 to generate ambient histogram data 1315. The ambienthistogram data comprises, without limitation, an intensity value foreach pixel within the evaluation ambient image, and state informationindicating whether a given pixel should be counted by a histogramfunction 1322. In one embodiment, the strobe influence functionimplements an intensity discriminator function that determines whether apixel is sufficiently illuminated by a strobe to be precluded fromconsideration when determining an ambient exposure coordinate. Oneexemplary discriminator function is true if a pixel in evaluationambient image 1312 is at least as bright as a corresponding pixel inevaluation strobe image 1310. In another embodiment, the strobeinfluence function implements an intensity discriminator function thatdetermines a degree to which a pixel is illuminated by a strobe. Here,the strobe influence function generates a weighted histogramcontribution value, recorded in histogram function 1322. Pixels that arepredominantly illuminated by the strobe are recorded as having a lowweighted contribution for a corresponding ambient intensity by thehistogram function, while pixels that are predominantly illuminated byambient light are recorded as having a high weighted contribution for acorresponding ambient intensity by the histogram function.

In one embodiment, the first evaluation coordinate comprises a defaultcoordinate. In another embodiment, the first evaluation coordinatecomprises a coordinate identified by a user, such as via a tap gesturewithin a preview image. In yet another embodiment, the first evaluationcoordinate comprises a coordinate identified via object recognition,such as via facial recognition.

Histogram function 1322 accumulates a histogram 1317 of ambient pixelintensity based on ambient histogram data 1315. Histogram 1317 reflectsintensity information for regions of evaluation ambient image 1312 thatare minimally influenced by strobe illumination. Regions minimallyinfluenced by strobe illumination comprise representative exposureregions for ambient exposure calculations.

An image search function 1324 scans evaluation image 1312 to select theambient target exposure coordinate, which may subsequently be used as anexposure coordinate to sample an ambient image. In one embodiment, thesubsequently sampled ambient image and a subsequently sampled strobeimage are combined in accordance with the techniques of FIGS. 2A through10B.

In one embodiment, the image search function 1324 selects a coordinatethat corresponds to a target intensity derived from, without limitation,intensity distribution information recorded within histogram 1317. Inone embodiment, the target intensity corresponds to a median intensityrecorded within histogram 1317. In another embodiment, the targetintensity corresponds to an average intensity recorded within thehistogram 1317. In certain embodiments, image search function 1324preferentially selects a coordinate based on consistency of intensity ina defined region surrounding a given coordinate candidate. Consistencyof intensity for the region may be defined according to any technicallyfeasible definition; for example, consistency of intensity may bedefined as a sum of intensity distances from the target intensity forpixels within the region.

In one embodiment, frame-level color correction factors, discussed inFIG. 4B above are substantially derived from regions included in ambienthistogram data 1315.

FIG. 13B is a flow diagram of method 1302 for selecting an exposurecoordinate, according to one embodiment of the present invention.Although the method steps are described in conjunction with the systemsof FIGS. 1A-1D, persons skilled in the art will understand that anysystem configured to perform the method steps, in any technicallyfeasible order, is within the scope of the present invention. In oneembodiment, method 1302 implements an exposure coordinate selectionfunction, such as data flow process 1300 of FIG. 13A.

Method 1302 begins in step 1350, where the exposure coordinate selectionfunction receives an ambient evaluation image and a strobe evaluationimage from a camera subsystem. The ambient evaluation image and thestrobe evaluation image may be of arbitrary resolution, including aresolution that is lower than a native resolution for the camerasubsystem. In one embodiment, the ambient evaluation image and thestrobe evaluation image each comprise one intensity value per pixel.

In step 1352, the exposure coordinate selection function selects animage coordinate. The image coordinate corresponds to a two-dimensionallocation within ambient evaluation image, and a corresponding locationwithin strobe evaluation image. Initially, the image coordinate may beone corner of the image, such as an origin coordinate. Subsequentexecution of step 1352 may select coordinates along sequential columnsin sequential rows until a last pixel is selected. In step 1354, theexposure coordinate selection function computes strobe influence for theselected coordinate. Strobe influence may be computed as describedpreviously in FIG. 13A, or according to any technically feasibletechnique. In step 1356, the exposure coordinate selection functionupdates a histogram based on the strobe influence and ambient intensity.In one embodiment, strobe influence comprises a binary result and anambient intensity is either recorded within the histogram as a countvalue corresponding to the ambient intensity or the ambient intensity isnot recorded. In another embodiment, strobe influence comprises a valuewithin a range of numeric values and an ambient intensity is recordedwithin the histogram with a weight defined by the numeric value.

If, in step 1360, the selected image coordinate is the last imagecoordinate, then the method proceeds to step 1362, otherwise, the methodproceeds back to step 1352. In step 1362, the exposure coordinateselection function computes an exposure target intensity based on thehistogram. For example, a median intensity defined by the histogram maybe selected as an exposure target intensity. In step 1364, the exposurecoordinate selection function searches the ambient evaluation image fora region having the exposure target intensity. This region may serve asan exemplary region for a camera subsystem to use for exposing asubsequent ambient image. In one embodiment, this region comprises aplurality of adjacent pixels within the ambient evaluation image havingintensity values within an absolute or relative threshold of theexposure target intensity. The method terminates in step 1370.

FIG. 13C illustrates a scene 1380 having a strobe influence region,according to one embodiment of the present invention. The strobeinfluence region is illustrated as regions with no hash fill. Suchregions include a foreground object 1384 and a surrounding region wherethe strobe illumination dominates. Region 1382, illustrated with a hashfill, depicts a region where strobe influence is minimal. In thisexample, pixels from region 1382 would be preferentially recorded withinthe histogram of FIG. 13B. In one embodiment, pixels comprising thestrobe influence region would not be recorded within the histogram. Inone alternative embodiment, pixels comprising the strobe influenceregion would be recorded within the histogram with reduced weight.

FIG. 13D illustrates a scene mask 1390 computed to preclude a strobeinfluence region 1394, according to one embodiment of the presentinvention. In this example, pixels within the strobe influence region1394 are not recorded to the histogram of FIG. 13A, while pixels outsidestrobe influence region 1394 are recorded to the histogram.

FIG. 14 is a flow diagram of method 1400 for sampling an ambient imageand a strobe image based on computed exposure coordinates, according toone embodiment of the present invention. Although the method steps aredescribed in conjunction with the systems of FIGS. 1A-1D, personsskilled in the art will understand that any system configured to performthe method steps is within the scope of the present invention. The goalof method 1400 is to pre-compute two or more camera subsystem exposureparameters, a time consuming process, prior to actually samplingcorresponding images for a photographic scene. Sampling thecorresponding images is a time-sensitive process because the more timebetween two different images, the more likely the two correspondingimages will appear. Therefore, the goal of method 1400 is to reduceoverall inter-image time by performing time-consuming tasks related toimage sampling prior to actually sampling the ambient image and strobeimage. An image set comprises at least one ambient image and at leastone strobe image. A camera control function is configured to executemethod 1400. In one embodiment, the camera control function comprises acomputer program product that includes computer programming instructionsembedded within a non-transitory computer readable medium, such aswithin NV memory 116 of FIG. 1A, wherein the computer programminginstructions cause a processor to perform method 1400.

Method 1400 begins in step 1410, where the camera control functioncauses a camera subsystem, such as camera unit 130, to sample an ambientevaluation image using available ambient scene illumination. The ambientevaluation image may be sampled at any technically feasible resolution,such as a lower resolution than a native resolution for the camerasubsystem. In step 1412, the camera control function causes the camerasubsystem to sample a strobe evaluation image of the photographic sceneusing a strobe illumination device, such as strobe unit 136. In oneembodiment, a default exposure coordinate, such as an image midpoint, isused by the camera subsystem for exposing the ambient evaluation imageand the strobe evaluation image. In another embodiment, an exposurecoordinate selected by a user, such as via a tap selection gesture, isused by the camera subsystem for exposing the ambient evaluation imageand the strobe evaluation image. In alternative embodiments steps 1412and 1410 are executed in reverse sequence, so that the strobe evaluationimage is sampled first followed by the ambient evaluation image. A givencoordinate may also include an area, such as an area of pixelssurrounding the coordinate.

In step 1414, the camera control function enumerates exposurerequirements for an image set comprising two or more related images. Oneexemplary set of exposure requirements for an image set includes arequirement to sample two images, defined to be one ambient image andone strobe image. The ambient image exposure requirements may include anexposure target defined by a histogram median of pixel intensity valuesidentified within the ambient evaluation image and strobe evaluationimage. The exposure requirements may further include a coordinate beingdominantly illuminated by ambient illumination rather than strobeillumination. The strobe image exposure requirements may include anexposure target defined by a user selected coordinate and a requirementto illuminate a scene with strobe illumination. Another exemplary set ofexposure requirements may include three images, defined as two ambientimages and one strobe image. One of the ambient images may require anexposure target defined by a histogram median with a positive offsetapplied for pixels identified within the ambient evaluation image andstrobe evaluation image as being dominantly illuminated via ambientlighting. Another of the ambient images may require an exposure targetdefined by a histogram median with a negative offset applied. The strobeimage exposure requirements may include an exposure target defined bythe user selected coordinate and the requirement to illuminate the scenewith strobe illumination. Upon completion of step 1414, a list ofrequired images and corresponding exposure requirements is available,where each exposure requirement includes an exposure coordinate.

In step 1420, the camera control function selects an exposure coordinatebased on a selected exposure requirement. In one embodiment, theexposure coordinate is selected by searching an ambient evaluation imagefor a region satisfying the exposure requirement. In step 1422, thecamera control function causes the camera subsystem to generate camerasubsystem exposure parameters for the photographic scene based on theselected exposure coordinate. In one embodiment, the camera subsystemexposure parameters comprise exposure time, exposure sensitivity (“ISO”sensitivity), aperture, or any combination thereof. The camera subsystemexposure parameters may be represented using any technically feasibleencoding or representation, such as image sensor register valuescorresponding to exposure time and exposure sensitivity. In step 1424,the camera subsystem exposure parameters are saved to a data structure,such as a list, that includes image requirements and correspondingexposure parameters. The list of image requirements may include an entryfor each image within the image set, and each entry may include exposureparameters. In certain embodiments, the exposure parameters may be keptin a distinct data structure. The exposure parameters for all imageswithin the image set are determined prior to actually sampling theimages. If, in step 1430, more camera subsystem exposure parameters needto be generated, then the method proceeds back to step 1420, otherwise,the method proceeds to step 1432.

In step 1432, the camera control function causes the camera to sample animage of the photographic scene based on a set of camera subsystemexposure parameters previously stored within the list of imagerequirements. In step 1434, the camera control function causes the imageto be stored into the image set. The image set may be stored in anytechnically feasible memory system. If, in step 1440, more images needto be sampled, then the method proceeds back to step 1432, otherwise themethod terminates in step 1490.

The list of image requirements may comprise an arbitrary set of ambientimages and/or strobe images. In certain alternative embodiments, thestrobe evaluation image is not sampled and method 1400 is practicedsolely over images illuminated via available ambient light. Here, ahistogram of ambient evaluation image may be used to generate exposureintensity targets in step 1414; the exposure intensity targets may thenbe used to find representative coordinates in step 1420; therepresentative coordinates may then be used to generate camera subsystemexposure parameters used to sample ambient images.

In certain embodiments, the camera subsystem is implemented as aseparate system from a computing platform configured to perform methodsdescribed herein.

In one embodiment step 1420 of method 1400 comprises method 1302. Incertain embodiments, step 612 of method 600 comprises method 1400. Inone embodiment, step 612 of method 600 comprises method 1400, step 1420comprises method 1302, and step 616 comprises method 1000. Furthermore,step 1012 comprises method 1002. In certain embodiments, step 1014comprises method 1100.

In summary, techniques are disclosed for sampling digital images andblending the digital images based on user input. User interface (UI)elements are disclosed for blending the digital images based on userinput and image characteristics. Other techniques are disclosed forselecting UI control elements that may be configured to operate on thedigital images. A technique is disclosed for recommending blend weightsamong two or more images. Another technique is disclosed to generating aset of two or more camera subsystem exposure parameters that may be usedto sample a sequence of corresponding images without introducingadditional exposure computation time between each sampled image.

One advantage of the present invention is that a user is providedgreater control and ease of control over images sampled and/orsynthesized from two or more related images.

While the foregoing is directed to embodiments of the present invention,other and further embodiments of the invention may be devised withoutdeparting from the basic scope thereof, and the scope thereof isdetermined by the claims that follow.

We claim:
 1. A device, comprising: a non-transitory memory storinginstructions; and one or more processors in communication with thenon-transitory memory, wherein the one or more processors execute theinstructions to: load two or more source images including at least onestrobe image and at least one ambient image; color-correct at least onepixel of the two or more source images based on a chromatic attractorfunction or a trust-factor; initialize a first blend weight associatedwith the two or more source images; and render a first combined imagefrom the two or more source images based on the color-correction and thefirst blend weight.
 2. The device of claim 1, wherein the device isconfigured such that the color-correction is applied to the at least onestrobe image.
 3. The device of claim 1, wherein the one or moreprocessors execute the instructions to estimate a frame-level correctionfor at least one of the two or more source images, the frame-levelcorrection based on at least one of a red correction, a greencorrection, or a blue correction.
 4. The device of claim 1, wherein theone or more processors execute the instructions to: compute a costfunction for the first combined image by interpolating one or moreattributes for each of the two or more source images, where the one ormore attributes includes at least one of a low intensity mark, a highintensity mark, or a half intensity value; and determine that the costfunction is minimized.
 5. The device of claim 4, wherein the device isconfigured such that the cost function is computed from at least one of:a plurality of median values from each of the two or more source images,or a sum of a distance from the low intensity mark to a first halfintensity value, and a distance from the high intensity mark and asecond half intensity value.
 6. The device of claim 1, wherein the oneor more processors execute the instructions to display the firstcombined image and a user interface element associated with the firstcombined image, the user interface element including a control element.7. The device of claim 6, wherein the device is configured such that aposition of the control element includes an offset estimate based on auser preference or a history of control element overrides.
 8. The deviceof claim 1, the one or more processors execute the instructions toestimate a patch-level correction, wherein the patch-level correction isbased on correcting a region of the at least one strobe image to beconsistent with an overall color balance with an associated region ofthe at least one ambient image.
 9. The device of claim 1, wherein thedevice is configured such that the first blend weight is a function of auser interface element, and modifying the user interface elementoverrides the first blend weight.
 10. The device of claim 1, wherein theone or more processors execute the instructions to compute a costfunction for the first combined image.
 11. The device of claim 10,wherein the device is configured such that the cost function isproportional to an area of the two or more source images, the areaincluding a subset of the two or more source images that is eitheroverexposed or underexposed.
 12. The device of claim 10, wherein thedevice is configured such that the cost function is based on a sum whereeach pixel within the combined image adds a value to the cost functionif a pixel intensity is below a low threshold or above a high threshold.13. The device of claim 10, wherein the device is configured such thatthe cost function is based on a sum where each pixel within the combinedimage adds an increasing value to the cost function in proportion topixel intensity.
 14. The device of claim 13, wherein the device isconfigured such that as the pixel intensity increases above a highthreshold or as the pixel intensity decreases below a low threshold, anincreasing cost value is added to the cost function.
 15. The device ofclaim 14, wherein the device is configured such that the high thresholdis ninety percent (90%) of maximum defined intensity for each pixel andthe low threshold is ten percent (10%) of the maximum defined intensityfor each pixel.
 16. The device of claim 10, wherein the device isconfigured such that the cost function includes a repulsion cost,wherein the repulsion cost increases the cost function as a userinterface element approaches a preconfigured anchor point of the userinterface element.
 17. The device of claim 10, wherein the device isconfigured such that the cost function includes an attraction cost,wherein the attraction cost decreases the cost function as a userinterface element approaches a preconfigured anchor point of the userinterface element.
 18. The device of claim 1, wherein the device isconfigured such that the first blend weight is based on exposurecoordinates of the two or more source images, the exposure coordinatesbeing selected based on searching the two or more source images for acoordinate that satisfies a corresponding exposure requirement.
 19. Acomputer program product comprising computer executable instructionsstored on a non-transitory computer readable medium that when executedby a processor instruct the processor to: load two or more source imagesincluding at least one strobe image and at least one ambient image;color-correct at least one pixel of the two or more source images basedon a chromatic attractor function or a trust-factor; initialize a firstblend weight associated with the two or more source images; and render afirst combined image from the two or more source images based on thecolor-correction and the first blend weight.
 20. A computer-implementedmethod, comprising: loading, using a processor, two or more sourceimages including at least one strobe image and at least one ambientimage; color-correcting, using the processor, at least one pixel of thetwo or more source images based on a chromatic attractor function or atrust-factor; initializing, using the processor, a first blend weightassociated with the two or more source images; and rendering, using theprocessor, a first combined image from the two or more source imagesbased on the color-correction and the first blend weight.